Microscopic Explorations Exercises
The LHS/MSA guide, 'Microscopic Explorations' provides a basic set of tested, reliable exercises, presented in an "inquiry science" context. Its ten topics, however, are only an introduction to the microworld. Look at the Project MICRO's two bibliographies for many other possibilities (don't miss the listings for 'Private Eye' and 'Nanoscale Science'). The website list that ends the 'Microscopy' booklist even lists several laboratories that provide remote-access scanning electron microscopy for K-12 classes.
If you don't find the lesson that you want, you may be tempted to write your own. To quote Project RISE of the National Academy of Science, "Unlike the other roles for scientists, ... a role in developing instructional materials for K-12 science education is suitable only for a few individuals. Many of those involved in improving science education advise scientists who are interested in developing materials, 'DON'T DO IT!'." You'll find good reasons presented in the RISE website.
The Beanie Baby Mystery
There are exceptions to every rule, of course. MICRO features here material that provides a direct extension of the content of 'Microscopic Explorations'. Our first activity, 'The Beanie Baby Mystery', written by microscopist-volunteer Joe Nielley of Abbott Labs, is a good example; it's a direct extension of the 'Kitchen Powders' unit of Microscopic Explorations. Read it at http://www.microscopy.org/education/projectmicro/beaniebaby.cfm
Project MICRO Sand Box
The Project MICRO Sand Box is an outgrowth of Activity 8 of Microscopic Explorations. You can request free samples for classroom use - please contribute your own sand to keep this service going.
Tool for Hand Sectioning Fresh Tissue
A detailed PDF about hand sectioning fresh tissue can be requested from Rosemary.White@csiro.au How to make a hand microtome from a thread spool is described at http://www.microscope-microscope.org/activities/school/microtome.htm. You'll find a wealth of similar useful advice in Oxlade & Stockley's "The World of the Microscope". See the MICRO Microscopy booklist for details.
Molecular Expressions, the excellent Florida State University microscopy site offers K-12 lessons at http://micro.magnet.fsu.edu/primer/resources/k12.html
American Society for Microbiology
Many detailed lesson plans on microscopy, lenses, cell structure, and DNA are available from the American Society for Microbiology at https://www.asm.org/index.php/educators/k-12-classroom-activities.
Microscope Lab Journal
A PDF for a microscopy lab notebook data page is available here http://www.greatscopes.com/journal.htm; teachers can make copies for class use.