Announce to your students that you are going to lead them in an experiment. Show them a rotten banana and ask them if they would eat it. Then tell them they are going to conduct an experiment to observe how quickly bananas ripen under different conditions. This will lead them to make conclusions about the optimum conditions in which bananas should be kept. Explain that a big fruit company, Chiquita Banana, paid a consulting company to find a way to keep bananas fresh longer. Challenge the students to find some of their own effective ways to accomplish this.
Display four bunches of bananas to the class. Choose green ones, so that you can be sure the bananas share the same amount of ripeness. Divide your class into four groups, and give each of them one bunch of bananas (along with a warning not to eat them). Tell each group they will be watching their bunch of bananas daily to see how fast they ripen.
Ask the first group of students to place its bunch of bananas in a paper bag, and the second group in a plastic bag. The third group should put a bunch in a refrigerator (you can bring in an apartment-sized refrigerator for the experiment, or use the refrigerator in the teacher's lounge). The fourth group should hang the bananas on a banana stand and leave them in the classroom on your desk.
Lead a class discussion each day as the groups report on the brownness of their bananas. This may cause some disagreement because the students won't have any measure other than their own observations. Explain that careful observation is an important part of the scientific method, and allow for some disagreement in the classroom about which bananas are turning brown the fastest.
Evaluate the results. Someone's bananas will turn brown, and even black, long before the others. Ask the students to make some educated guesses about why the bananas in the refrigerator turned brown before all the others. Also rank the bananas in the paper bag, the plastic bag and on the banana stand. You can even make a chart showing the rates at which each of these samples turned brown.
Celebrate the success of the experiment by serving every student some banana pudding.