Teach the ballerina to dance like Scratch! Scratch has an extra step in his dance. Have the ballerina copy his steps exactly. This uses a broadcast technique where Scratch 'tells' the ballerina what to do next.
This little project introduces the concept of inter-process communication. Beside fixing the dance step, you could introduce more steps, to see how the ballerina responds. Remember, the ballerina is being told what to do next. Adding a music sound track to the drum clicks would be an interesting math challenge to get the dancers to dance with the music's tempo.