We thought the game should have about 20 levels before we released it in the iTunes App Store, and we had about 10 levels already done.
I took the strategy of teaching something new in one level (such as how to use the jetpack), repeating something they already knew from a prior level (just avoiding animals) in the next level, and then having them use the new skill (like the jetpack) in the subsequent level. Hence: learn something new, review something you learned before, practice what you just learned. This method of teaching is used quite often when mastering a new language.
The students thought of logic puzzles, such as matching up species:
Balancing a glass of soda on the roof of you car, so if you turn too fast, it will spill:
Or putting in a dead-end that is tempting, but won’t work (you hear the prizes first, so you aim for those, only to find out the road ends). The correct path is to the right:
They also thought of a lake that would require you to get a sail, put the sail on the sail boat, then blow (at the front of the iPad where the microphone is) to get the boat across the lake:
As you can see, it’s easy to come up with ideas for new levels. What’s not so easy is implementing them (through programming).