If you don't want to make a full tassel to add to a graduation cap favor, another option is to use a single piece of thicker string, such as satin cord intended for jewelry crafts, and fray the ends a bit to look more like a tassel.
It is square and stiff, being made of a framework of cardboard covered with cloth or silk; on the top, along the sutures of the stuff, are three or four raised, board-like, arched ridges, at the junction of which in the centre is a knob or tassel (floccus).
Use more glue or pushpins to add fun mementos from their school days such as a tassel from a graduation cap, a copy of a locker key, a ticket from a special sporting event, or a dried flower from prom night.
Tassel Tree (Acacia) - Beautiful shrubs and trees, thriving in warmer countries, but a few grown out of doors do well in parts of England.
Graduates can purchase a cap, gown and tassel package, souvenir tassels, diplomas, graduation announcements, and even fun accessories like a tassel key ring and a graduating stuffed bear.