You could do a lesson on flag/sheild/heradly design. Have the students
create their own family crest. I would not paint the posterboard. Either use
colored poster board or have them do a white background and used construction
paper for the design.. The colors will be stronger and you won't have the drying
time of paint.
Also....I would not use glitter in the gym! I know our gym teachers hate it
when there is glitter anyway (no problem for me as i am not a big glitter
fan!). It is very hard to get it all up! You might use a glitter glue or glitter
paint if you want that sparkle of glitter but not the mess. I would forget
the glitter all together. You could use metalic or shiny paper.