No living animal besides maybe a snail is likely to survive in there. We did the same thing with guppies in 5th grade and maybe 2 survived. You should explain to your teacher how this does not work in a CLOSED ecosystem and how it is in fact animal cruelty. Please do not use a betta or any other fish for that matter. BETTAS DO NOT LIVE IN MUD PUDDLES! They are also carnivores and will likely starve if only given plants to eat, and no they can't go a month without food.
My advice: BOYCOTT, BOYCOTT, BOYCOTT, BOYCOTT!!!!!!!!!!!! This IS animal cruelty and that teacher is setting a terrible example for the class. No animal should be made to live in these conditions. I wish I had known more when I took the class so that I could have stopped it. You can't get in trouble for voicing your opinion, so please try to stop this.