I feel like this would have benefited a LOT from some story/tutorial or other directions in the game itself. The music is hauntingly good and I could play it on a loop all day long though. Also, the spawn rate could use some boosting. By the time the enemies started showing up with any frequency I already had more towers than I knew what to do with them.
EDIT: Turns out I had the slow spawning bug without realizing it. A refresh tweaked the difficulty settings quite a bit :D
This looks like it has a TON of potential but you just ran out of time to hit the marks with some of the criteria in the theme and educational value. I'm excited to revisit if you keep going with it.