Harp- Box and Rubber Bands
A project I remember from childhood is putting rubber bands of different widths around a sturdy open box (such as a shoebox) to make a harp. That wouldn't be a very long project in and of itself, but you could decorate the boxes. The rubber bands can be "tuned" by making the part over the opening tighter or looser.
Check out how to make this "rubberband harp" at https://feltmagnet.com/crafts/...nd-Elastic-Band-Harp Instead of just gluing the harp together, use glue and clear tape to speed up the process and make it usable during classtime.
Write a psalm verse on the "harp" or surround the box with key verses.