Other Gab: Why Do Demos?

Last year was the first year in 10 years that my teaching assignment involved teaching Chemistry. As a cross-over to Chemistry, there was much to re-learn, much to develop, much to get accustomed to.  As they say "You can't do it all" and I most certainly didn't. What was most lacking in my teaching of chemistry was a repertoire of effective demonstrations. When I received the same assignment of teaching two sections of chemistry during this school year, I made a pledge to myself to do a demonstration each day (at least each day in which there wasn't a lab experience). My thought was that my students should be doing chemistry and seeing chemistry on a daily basis.  Every day should include chemistry; not just talk about chemistry or calculations about chemistry, but actual chemistry. Chemical reactions should happen. Chemical properties should come alive.  After all, it's a science class and science should be happening.


There's no doubt about it!  Students love chemistry demonstrations.  And physics demonstrations. And any science demonstration.  And I love them too!  Who couldn't love a science demonstration?  Science museums stay in business not because there are a bunch of people inside showing PowerPoint slides; and not because there is an opportunity to sit around tables solving stoichiometry or projectile problems; and not because there are booths where you can sit down and balance chemical equations or draw free-body diagrams.  Rather, science museums stay in business because there are interesting things to look at, to watch, and to interact with. And when these things happen, people learn.  And the learning that does happen is more closely tied to the content which is being learned; it is not abstracted, detached, nor remote.


Students love demonstrations.  They enjoy them.  But do they learn from them? Now that's a tough question.  And an important one.  After all, my science class should be about more than just having fun.  It should be more than entertainment.  If my professional goals centered around providing fun and entertainment for others, then I should have sought to obtain a job at a museum.  Or at a zoo. Or in a circus. But my professional aspirations are centered around educating high schoolers and that naturally landed me a job in a high school teaching science.


In addition to a couple of lab experiences, there were three noteworthy demonstrations this week in my chemistry class. On Monday, we were talking about solubility and saturation of solutions.  To demonstrate a supersaturated solution, a hunk (new measurement unit) of sodium acetate was placed in a beaker of 10 mL of water.  It was heated and heated and eventually dissolved; there's a definite chemistry lesson in this.  Then the solution of dissolved NaAc (as it is affectionately known) is poured into a clean buret;  it cools over the next 30 minutes as we discuss variables effecting solubility, solubility curves, unsaturated vs. saturated vs. supersaturated solutions, etc. Near the end of class we return to the back of the room. The solution drips from the buret onto a watch glass with a single crystal of NaAc.  Students watch in amazement as the dissolved NaAc immediately crystallizes, forming a tall column of undissolved solid.  (View picture.) Entertaining? Defintely!  Enjoyable? Clearly. Educational? Potentially.  For certain, the entire cycle of dissolving the NaAc at high temperatures, allowing for supersaturation through cooling, and ultimately the crystallization of the NaAc as it dripped from the buret was the bridge which connected the content of the lesson to the real world of chemistry.  Thanks to the demo, the content was no longer abstracted, detached nor remote;  rather, it was alive and happening before their very eyes.  Big bang. Big buck.


As a St. Patrick's Day demonstration this past Wednesday, some boric acid was dissolved in methanol, squirted on a lab table in the shape of a shamrock and lit.  For 20-30 seconds, a green flame in the shape of a shamrock emerges from the lab table. The green of the flame is a characteristic of boron's emission spectra.  Students responded immediately: "Cool" "Wow!"  "OMG" "Do it again!" After three more repetitions and about three more minutes, students were back in their seats cranking out molarity calculations. Little bang, little buck. This is a demo that's mostly entertainment. Definitely fun. (And unfortunately it did leave with a lot of leftover boric acid and methanol.)


On a third day this week in chemistry class, I complemented a lesson on molarity and dilution with a demonstration in which two solutions were made by dissolving a known amount of copper chloride in a 200 mL volumetric flask of water.  Lab techniques were demonstrated and students calculated the concentrations.  One solution was five times the concentration of the other. We noted the color of the two solutions; that was a separate lesson in itself.  Then I took out 40 mL of the more concentrated solution and placed it in a third 200 mL volumetric flask;  we calculated the moles of copper chloride present in that 40 mL.  Then I added water to this 40 mL to fill the flask to the 200 mL mark.  As I added the water, I asked students how much copper chloride was I presently adding;  they all agreed - none.  When finished diluting the solution, I asked students to calculate the concentration.  We all agreed that the new concentration was the same as the concentration of the more dilute solution; we noted the color.  I discussed the concept of dilution, dilution calculations and a dilution factor.  I thought this was big bang.  Attachment of content to real world. The dilution concept from the textbook coming alive. A chance to discuss good lab technique. A chance to demonstrate the types of questions which a chemist asks. A chance to see chemistry happen. Entertaining? Not really.  Enjoyable? I enjoyed it; my students would rather be watching green flames or see a column of NaAc grow tall. Educational?  Potentially.


Why do demos? is the question I am pondering.  Why skip demos? is a question which is easy to answer.  They take time to prepare. (Planning, practicing and preparing the dilution demo took me close to 50 minutes. Preparing and practicing the NaAc demo took me a half hour.) They take time to clean up and sometimes they are a pain to clean up. (The boric acid is mildly toxic; methanol causes blindness if ingested; and my St. Patricks day demo left me with an extra 200 mL of toxic mess to dispose of.) They cost money (equipment, materials, chemicals). They take class time to perform.  Sometimes they don't work as intended and I get embarrassed (but a good humbling isn't always a bad thing). Sometimes its difficult to think of a demo appropriate to the current topic. (The combustion of the methanol with the boric acid doesn't exactly have a solution theme.) And sometimes we believe that the class time spent showing students demonstrations could be put to better use by doing more educational activities, which usually means doing more drill and practice type work. (For certain, in the time it took me to mix two solutions and then dilute one to the concentration of the other, I could have done at least twice as many molarity and dilution problems.)  So if Why skip demos? is a question which quickly evokes some valid answers (or at least some appealing answers), then Why do demos?


As I was cleaning up my mess after class on Thursday, my demo a day commitment came under personal scrutiny. Was there any value to what I was doing?  Was I getting any bang for my buck?  Why was I exhausting myself with demos?  I walked back to the office pondering these questions. When I arrived in my office I observed Mrs. S at her desk.  Mrs. S is a veteran in the trade of doing demonstrations. Mrs. S is a chemistry teacher in our department who has a reputation among her colleagues and her students for loving demonstrations. Mrs. S is definitely a demo a day teacher. And to her credit, she does her demonstrations with flare (no pun intended).  As there should be, there is a sense of entertainment, even theatre, when Mrs. S does chemical demonstrations.  This is not to say that there is no learning going on;  it is simply to say that the learning occurs in an environment which captivates her lower-level chemistry students. Her students are hooked!  What teacher wouldn't want that?


Hoping for some encouragement, I posed the Why do demos? question to Mrs. S. Without hesitation, she gave me what seemed to be 30 answers to the question. Here is her take on the question:

• Demonstrations provide a sort of "visual cement" for a science course; they provide visual reinforcement of the content material.
• Students will most likely remember the material which is demonstrated. When they reminense about your class, they won't be thinking about worksheets, tests, or PowerPoint slides; they will be remembering your demonstrations.
• Demonstrations bring the textbook material to life and provide relevant application of the content.
• Demonstrations address the need to appeal to the varying learning modalites of students.  For many students, seeing is believing and seeing is learning.
• Demonstrations provide a avenue for critical thinking as they often naturally lead to the question why does this happen?
• Demonstrations pique student curiosity; students become more invested when their curiosity is piqued.
• Demonstrations provide an interesting diversion amidst an otherwise drab lesson plan, providing students with an interesting chunk to chew.
• Committing oneself to doing demonstrations encourages a teacher to grow professionally as they learn new ways to present and reinforce content material.
• Demonstrations are FUN - for both teachers and students.  They create an atmosphere of exciting inquiry within the classroom.

Shortly after having finished her list, Mrs. S began to bolt out of the office towards the prep room to prepare her upcoming rendition of a chemical demonstration.  Out of the corner of my eye, I observed her tie-dye lab coat flash by me.  I stopped her and asked if she would be interested in my left-over methanol-boric acid solution.  As a veteran of the trade, she knew exactly what it was for. She gladly accepted my offer. And I was quite relieved to have pawned it off on her.  Whew! What a relief.


The rest of my lunch period and prep period was busy as I prepared for my afternoon physics sections.  I had little time to continue my ponderings until 5 minutes into my first afternoon physics class;  the fire alarms sounded and the whole school was evacuated.  This gave me a few more minutes of further ponderings on the topic of why do demos? As is usually the case, the fire alarm was a false call and we returned to our classed to finish the school day.  


On my 30-minute trek home from school, my car ride thoughts returned to why do demos? I began to think about all those former students, who when reminsicsing about their experience in my course, would inevitably make a comment pertaining to demonstrations.  I've never heard such a student make comments like "I remember that one PowerPoint presentation on inertia" or "Have you designed anymore cool worksheets for your students to do" or "Do you still use that one Powerpoint presentation on ..."  No! Never!  This is not what my former students remember. The record is clear; they make comments like "I still remember that one demonstration when you made the aluminum rod make a sound by stroking it with your hand" or "Have you come up with any new demonstrations to show your students" or "Do you still do that demonstration when you shoot the falling monkey with your projectile launcher?" Students remember my demonstrations and your demonstrations for a reason. Demonstrations are meaningful; they stick in their heads.  Demonstrations are visual; they can't forget them.  Demonstrations are engaging; they hook kids attention. Demonstrations provide the connection between the concepts we are talking about and the material world which those concepts seek to describe.


Demonstrations are probably the closest thing in our profession to edutainment. They are an engaging and (at times) entertaining means of educating our students.  And they are an educational means of entertaining our students.  When a professional teacher transparently embeds a demonstration with the lesson content, students become engaged in the lesson.  Student investment in the lesson rises and And when the demonstration is presented using effective pedagogical strategies, higher rates of learning inevitably results.  A lesson immersed with showing students the operations of the material world is a lesson students will remember. Now what teacher wouldn't want that?


I got an email from Mrs. S the next morning: "By the way, one more reason to do demonstrations: total school evacuation." Now I am really glad I pawned the methanol-boric acid solution off on Mrs. S.  Better her than me.

How to Do a PLCU

[Editor's Note: The past several posts have focused in one way or another upon a common challenge confronting physics teachers.  The challenge involves getting students involved, engaged and invested in minds-on activity during hands-on laboratory activities. This post represents one teacher's efforts to salt the oats.]



The desire to make laboratory experiences appear to be meaningful to students caused me to rethink some of the methods by which they were evaluated about a decade ago. The desire of students to merely complete a set of directions without incorporating the relationships they were investigating was such an abhorrence, as was the copying that ensued, that I decided to make each discovery experience one of responsibility; the students were going to learn something and were expected to apply it.

The method by which this was done became know as the “Post-Lab Check Up” (plcu). Its intention was to make each student responsible to observe/collect data and discover and apply relationships. Their observations and results were organized in some fashion (sheet, notebook…) which were then used while responding to the questions related to the investigation. The goal is not for the student to have a complete understanding of the concepts at hand, but to use previously-acquired skills in new situations and make some sense of them.

This may appear to be similar to a “lab quiz” format, but the intentions are different. The plcu is intended to keep the student engaged with the activities of his or her group, experiencing mutual discovery. Since I started doing this a little over 10 years ago, very infrequently does any student refrain from involvement, a surprising change from the days when one student would dominate while the others copied. The copying that occurs now is almost always followed by “what does this mean?” or “how did you find that?” a far cry from the blatant plagiarism of the past.

Although improvement in attitude in the laboratory is valuable in itself, the Post-Lab Check Up serves a second purpose. It is well known that investigation followed by rehearsal is much more effective in making sense of the concepts at hand than investigation alone. Therefore I try to have the “check up” occur during the same class period. When this is not possible, it will occur at the beginning of the next period. While this may appear to be valuable since students can then spend the next few hours reviewing what they discovered, it is a rare event when a student spends any meaningful time unless there is an evaluative piece to complete such as data analysis, graphing…. In these situations, having the check up the next day is required.

The purpose of the post-lab check up is to provide a low key, non-intimidating experience for students, to encourage them to exert a sincere effort during lab investigations. I find this is accomplished by combining a completion grade with the plcu grade. As a result, a low plcu score, 4 out of 10 for example, will result in a 70% lab score as long as the student has been involved in the process. In the past, this is a typical grade for labs in which the student participated and appeared to complete the lab, but the data were poorly evaluated or collected. However, I do not use this for investigations that last several class periods and require a more formal write-up.



This week's article is contributed by Dave Smith. Dave is a graduate of Wheaton College in Wheaton, Illinois. He has been a high school physics teacher for 24 years. Dave is currently teaching Regular Physics and Honors Physics at Glenbrook South High School in Glenview, IL, where he has served since 1997.


Dave is sharing three examples of his many Post-Lab Check Ups.  The three examples are available for downloading and inspection:

• Waves at Boundaries
• Horizontally Thrown Projectiles
• Investigating Circuits

If you are a science teacher and have something to share, consider contacting the Lab Blab blog coordinator.  Your ideas could soon appear here on the Lab Blab and Other Gab pages.

Confessions of a Coattail Curber

I can't believe I said it.  They can't believe I said it.  Once more, I let careless words slip out of my mouth.  Like a dagger in the heart, they hit two of my favorite students with such force that their mouths dropped at a rate of 9-10 g's. How could I have been so insensitive? It took only five seconds; but in those five seconds I dashed Riley's and Ellen's hopes and dreams of another good lab. Seeing a group of six students crowded around a single table with only one set of equipment, I placed a molecular model kit on a separate table and said, "Riley and Ellen, let's have you come over here and work together."

Riley and Ellen's mouths opened wide.  It was as though I had broken the news that their best friend had died. Their faces immediately saddened, their postures changed and they even but-Mr-H-ed me. I've been teaching long enough to know that one! "But Mr. H, ..."  This but-Mr-H was noticeably different. There was a distinct trace of lowering intensity from the m-sound to the ch-sound accompanied by a little quivering along the way. This was a clear sign that I had crossed the line and they were VERY upset. Time seemed to stand still as they looked at me, looked at each other, looked at Lonnie, picked up their lab notebooks and slowly walk to the other lab table to work alone on their lab. It was at that point that I realized the dark truth about myself.  I am a coattail curber. 

There is six month's worth of evidence that shows that Riley and Ellen invariably gravitate to Lonnie's lab table.  All overt efforts on my part to vary the groups and to provide different partners and different experiences for students in labs are ultimately foiled by this sort of gravitation between Lonnie and Riley and Ellen.  The nature of this attraction seems to be related to Lonnie's tendency to understand the lab environment. Riley and Ellen's need to be partnered with a student who understands the purpose and is able to plot out a procedure, manipulate the equipment, collect the data, perform the calculations and reason towards a conclusion. As far as Riley and Ellen are concerned, their association with Lonnie is a match made in heaven. As for Lonnie, Riley and Ellen are among the nicest two students you could ever meet. A little bit of nice will go a long way towards providing a lot of helpin'.

It could be said that Riley and Ellen ride the coattails of Lonnie.  Their success in lab is largely due to the coattail effect. Coattail effect. A phrase borrowed from politics which Wikipedia describes as "a generic phrase for anyone that hangs onto another person as they forge ahead, without effort from the hanger-on." For certain, Riley and Ellen are hanging onto Lonnie as he forges ahead. The Free Dictionary describes the coattail effect this way: "to use your connection with someone successful to achieve success yourself." For certain, Riley and Ellen are successful in lab insofar as Lonnie is successful in lab.  But the most vivid description of a coattailer comes from The Urban Dictionary: "To sponge, mooch, free load, skate by, or do absolutely nothing but watch while somebody else does all the work and still somehow try to take at least partial credit for something you had no hand in."  When six students crowd around a single set of material at a lab table, there are going to be several students who do nothing but watch while somebody else does all the work.  And you can bet these students are going to take at least partial credit for something they had no hand in.  In suggesting that Riley and Ellen separate from Lonnie and the other three members at the lab table, I was preventing the coattail effect.  I was being a coattail curber.

Now I assure you that I meant no harm on that fateful Wednesday morning. My intentions were entirely innocent.  In fact, I actually intended to do good towards Riley and Ellen and the other members at the table.  It was not my intent to curb anything.  I simply wanted to promote increased engagement in the lab activity. My logic was simple: as the ratio of the quantity of hands to the quantity of lab sets is decreased, the level of engagement increases and the amount of learning increases. My formula for success was that the smaller the group size, the greater the engagement and the more profitable the lab experience.  So I was simply migrating from table to table in an effort to reduce the group sizes to two students.  But in doing so, I was curbing the ability of many students to achieve success on this lab by means of the coattail effect.  I was a coattail curber.

When I was in high school, I played basketball on the school team.  During nearly every practice there was a moment when the coach blew the whistle and shouted "Free Throws."  We all knew what to do.  The coach did not need to say anything else.  We all got a ball, paired up and went to one of the eight baskets around the gym to practice our free throws.  The formula for optimizing this experience was simple: two players, one set of equipment. The smaller the group size at every basket, the more beneficial the activity. If your free throw partner was ill or injured, you didn't triple up with two other teammates; rather you considered yourself fortunate to have a basket to yourself at which you would get more free throw practice. In my four years of playing high school basketball, I never witnessed six players congregating at a single basket, each waiting their turn to shoot free throws while there were empty baskets around the gym. This was just not a sensible way to occupy the time. And never once did the entire team crowd around the best free throw shooters basket and watch him shoot free throws for 10 minutes, considering each success of his as being their own. That would be ludicrous.

 In making an effort on that Wednesday morning to reduce the size of lab groups, I was exercising free throw practice logic.  Two students, one set of equipment, an optimized experience. Just two weeks earlier, I had done a Young's Experiment Lab in one of my physics classes.  I had one laser, one slide with a double slit, one screen and 25 students. That's 25 students using a single set of equipment.  I enjoyed watching 8-10 students cooperate (and at times, argue) as they attempted to collect data to determine the wavelength of light. But what I didn't enjoy is watching the inactivity of a dozen or more students as they sat unengaged on the side of the room as a spectator. At first, they were humored by the feud over which of the little red dots on the screen to use for measuring y. And many of them were quite entertained as several students argued about how much sag to allow in the measuring tape s they measured the distance from the screen to the double slit.  But soon they zoned out and turned into Delilahs.  Engagement turned into spectatorship and the coattailers quickly lined the sidelines. So when I made the effort to break up the groups of four and six into smaller groups of two students, I was simply attempting to optimize the experience for my students.  It was using free throw practice logic.

After some further resistance, Riley and Ellen crowded around their own set of molecular models and worked on the lab together as a twosome.  I periodically circulated through the lab over the course of the next 30 minutes.  Each time I passed by Riley and Ellen's station, I observed 100% engagement.  I also observed science talk, lots of thinking, growing confidence and great progress.  As the period ended, Riley and Ellen returned to the front of the room with a smile on their face and a sense of pride in their hearts.  Riley commented, "Mr. H, aren't you proud of us?  Ellen and I finished the lab on our own. Aren't you proud of us?"  I winked, smiled and affirmed,  "I knew you could do it. I AM proud of you."

As Riley and Ellen left the room that day, I thought to myself:  I'm proud to be a coattail curber. If I want my students engaged in doing science, I will have to provide environments which are conducive to engagement. And one aspect of such an engaging environment is group size.  While there may be occasions for which larger groups offer more benefit than smaller groups, I've observed that engagement generally increases when free throw practice logic is applied to group size. Especially for those very passive students who generally "sponge, mooch, free load, skate by, or do absolutely nothing but watch while somebody else does all the work", minimizing group size goes a long way towards increasing their engagement.

So the first very practical means of salting the oats involves curbing the coattail effect by limiting the group size.  Next week we explore one teacher's strategy for encouraging engagement and investment in lab activities which has shown positive gains even in situations in which the group size is more than desired.


This week's article is written by Tom Henderson.