Recently in my classroom, we did a simulation to show the effect of camouflage on the evolution of bugs (a variation of birds and worms from Project Learning Tree). In the past when I've facilitated these kinds of experiences, I've always ended up a little frustrated. These simulations work best when students operate without any personal preference or stubbornness. However, I teach middle school--students always interject personal preference and some stubbornness. In this particular activity, students acted as birds, collecting bugs (small pieces of colored paper) from various environments (colored paper backgrounds). Some students made it their mission to collect the bugs that were supposed to be camouflaged (i.e. they only collected the red bugs from the red background instead of picking the more apparent white bugs). At the end of the simulation, I would have been frustrated if I had not recently made a discovery: these kinds of simulations are MODELS--true models in the NGSS sense of the word. As imperfect models, these kinds of simulations are great opportunities to look for strengths and limitations. Identifying limitations of models first appears in the 3-5 grade band while evaluating the limitations of models appears in the middle school grade band. With limitations identified, students can take the analysis one step further and recommend changes to the model to correct some of the limitations. In my class, instead of my being frustrated and saying, "Here is what you should have seen. . ." we had a discussion about how the simulation represents "real life" and a discussion of limitations. What I initially feared was a failure, turned into a different kind of success.
This year, as you lead your students through simulations, don't forget that they are models that your students can evaluate.