Something like this. Not springy but rigid. They sometimes come in a set of increasing heights so you can train your jumping height/endurance/speed/etc. A great thing to have if he's at all interested in track and field, basketball, skateboarding, parkour, or really any sport that involves jumping.

I used to have a blast working on my jumping when I was in high school. It's a crazy good workout and feels good to progress in I think.

I know you can get them at Walmarts and Dick's if those exist where you are but they're sold many places I'm sure.