If it is due tomorrow, you've waited too long to ask help.
To do this kind of experiment you need to have
1. several pieces of glass, identical in shape and composition
2. several different methods of heat treating them
3. a way to safely test the strength of glass.
4. be reasonably certain that #2 didn't mechancially ruin the glass,
so the only thing being tested is the change in composition due to
heat (ie, if you cracked the glass heat treating it, that test is ruined)
#3 is usually a destructive test of some kind - I did those kinds of tests in my graduate research and the equipment we used isn't normally found in a highschool laboratory. It's not too fancy, it just is too specialized for most schools and possibly too expensive. The differences are probably small, so you need fairly sensitive equipment. A hardness test (as opposed to "strength") is a lot easier. There's a simple hand tool (name escapes me for the moment) that does something similar to hitting an awl with a mallet...it punches into your material and you can measure the dent made. Glass might be too hard for it, or too brittle though.
#2 requires a kiln or furnace of some kind. Some schools have this, usually to work on pottery or the like.
#1 will require buying glass samples, although something like a microscope slide might work nicely and be cheap and reasonably
Bottom line is...you needed to be thinking about all this a long time ago. Even if you had all the tools lined up (furnace, stress testing equipment, glass) it would take more time than you have just to perform the experiment, much less measure the results.