A compound microscope is only useful got looking at slides, which may get rather boring for students, slides must be purchased or made at home, which can be tedious and time consuming. A stereo microscope will enable your student to view live specimens, 3-D objects, and some slide use.
For normal observations, you probably will not need a microscope with a magnification higher than 400X. 400X magnification is generally the highest level students use in most high school courses.
Experiment Ideas:If you decide to purchase a stereo microscope you can fill a small plastic tray with pond water and have them look through the side of the container with the microscope. If you decide to purchase a compound microscope you can purchase plain slides and cover slips and make your own slides out of vegetable peels, plants, and other transparent 3-D objects.