I think that Beth Jones at Carnegie-Mellon worked with high school students from
her area. They developed exercises based on Ade and Trp auxotrophs,
UV sensitivity, and transformation that seemed very practical for high school.
The Genetics Society of America might have more details. The work that I saw was
presented at a 1993 Yeast meeting in Madison, Wisconsin.
David Perkins at Stanford has many lab exercises with Neurospora that illustrate
simple Mendelian features and might also be of interest.