Here's another easy challenge to expose students to linkages. Jumpers use the same 4-bar linkage as punchers, but are angled to push down to drive the mechanism up.

A LEGO hopping robot with legs based on a 4-bar linkage

They can be easily modified to jump straight up, or to hop in a direction by either changing the angle of the legs, or by orienting both legs forward like in the following video:

How else can your engineers make them hop forward? What methods result in the farthest hop?

For a more complicated challenge, jumpers can be motorized, which allows students to explore how the timing of the front and back legs affect hopping. Here's a video of a couple experiments - can your engineers figure out why delaying the front leg's jump causes the robot to hop forward?

This isn't a very robust build, more of a quick hack to test the impact of leg timing, so we didn't post build instructions. Maybe we will in the future if we put more work into building a robust hopper - or if your engineers come up with a better design - but for now you can find detailed pictures of this build here.