I saw this activity used in an elementary music classroom, I believe 3rd grade was the appropriate class for this project, though I might be wrong. In this exercise students are given four boxes connected to each other to represent a measure. Each student (or group) is given music notation that will only fit the number of boxes that correspond with the number of beats it gets. Ex: the half note sheet will fit in exactly two boxes.
This activity can be done individually or in groups. If in groups, students can break into groups of four and each create their own, then take turns clapping the rhythms they created. After this is completed, each group can perform their four-measure piece for the class (using clapping and rhythm syllables) or the class can learn the piece themselves.
Attached is an example of what the sheets might look like.