Instructor notes for Snow Stratigraphy.
Steve Custer
Earth Sciences, Montana State University, Bozeman, MT 59717-3480

Custer, S.G., 1991, Snow as a field-teaching medium for Earth Science: Journal of Geological Education, v 39, p. 34-43.

This reference might help you.  The wonderful thing about snow is that it is never the same at any site on two subsequent days.  There is always something happening.
Be prepared to observe with the students and thing with the students as you observe.
This is a field exercise and it is not rocks so the changes are fast, but don't forget that snow is a complete analog for igneous, sedimentary and metamorphic rocks, and that the
snow is an excellent analog for stratigraphy, complete with facies changes, thickness changes, and lithologic (snow changes).
This is a snow exercise so do NOT plan to do this if there is now snow where you live.

Have fun.  This exercise gets the students out in the field and the field can be right outside your school. 
You really do need a hand lense and a ruler and a notebook.  After that you can improvise as suggested in the reference above.