Immediately before the experiment, wash and peel onion bulbs for the class.
Remove the entire brown outer skin and cut the onion in half with a knife. Pull apart the layers of the onion. The thin, nearly transparent film layers within the onion will be used by the students.
Place the onion film into a Petri dish and then place this into the refrigerator until the students arrive.
Bring out the microscopes and set them on the lab bench.
Set the microscopes to the lowest magnification and plug them into an electrical outlet.
Clean the lenses with lens paper or laboratory wipes and test the knobs to make sure the lenses focus properly.
Make sure that the stage can be moved.