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

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