This activity works well for the classroom. Give each pair or group of students three test tubes and a minimum of six glucose test strips (it’s a good idea to have additional test tubes and glucose test strips available for further experimentation).
Cover the label of the lactase drops with paper or colored tape to hide the identity of these “mystery” drops from your students. Follow the instructions above but don’t reveal what the mystery drops are until the experiment is completed.
Tabulate all the results on the board so everyone can see them. Acknowledge that small variations between groups may exist (for example, most strips require reading at an exact time after dipping; if students do not follow the instructions exactly, results may vary slightly). Small variations are okay, as long as your initial controls were tested correctly.
Students may conclude that somehow the mystery drops converted something in the regular milk to glucose. This may be true, but at this point one other possibility cannot be ruled out—can your class think of what it is? If not, ask them how they know that the mystery drops aren't glucose.
Have someone in the class test the lactase drops. Unless the mystery drops (the lactase drops) themselves are tested with the glucose strips, no conclusions can be reached!
Add the result of this test to the data recorded on the board. Now what sort of conclusions can be drawn from the data?