A simple yet effective way for students to work on group ear training. Also useful for helping students figure out where "DO" is using key signatures when you print the staff lines on transparency pages.
Hang in the front of the room and use a pointer (baton/drum stick/etc...) to point out pitches and intervals you'd like the students to work on. You can start simple and add harder intervals as students become comfortable with listening and singing in tune with each other. Endless possibilities.
I printed the pages, cut and pasted them together and then glued them all to colored card stock and had it laminated for durability. The staff pages were printed on transparencies and glued together.