You could do a bunch of cool things. Most schools have a very small sample of radioactive material, which will be slowly emitting alpha particles. They probably have a geiger counter, which will count the particles, but it doesn’t let you see the tracks or investigate their properties. A spark chamber would be much cooler: you could see the tracks that the particles make across the chamber. You could measure the curvature of these tracks: from that it’s easy to work out the mass and charge of the particle, so you can work out what type of particle it is.
More exciting, in my view, is that you could detect high energy cosmic rays, and the particles like muons which they give off. The spark chambers I’ve seen show tracks from cosmic ray muons every few seconds. So you could do a bunch of things: measure how many of these particles are hitting the ground every second, study and observe their tracks and properties. It would be pretty cool.
Actually, we’re always looking for more background data from cosmic rays anyway. So all new spark chambers are of use to researchers on these things.