Breed fancy rats instead. Ball pythons are going to be difficult to incorporate into a classroom sort of setting - their generation gap is about 3 years, and it takes the entire year to feed, cycle, breed, get eggs, and then the eggs hatch. Your students might never even see the babies.
Find a local rat breeder, and pick up a blue rex rat, and a black standard coated rat that carries blue. Blue is a recessive trait, and rex is a codom trait. Breed the two together, and you'll get babies that'll display both traits (hopefully). Since rat color genetics have more than a few dimensions to them you can get more in depth with the variations. You can raise up the babies you get from the breeder in about 2-3 months (then they'll be large enough to breed and have a nice big litter), then you have a 3 week gestation, and then babies that'll be weaned at 5 weeks.
Any babies the students don't want to adopt can be snake food.
~jenny
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"We call them dumb animals, and so they are, for they cannot tell us how they feel, but they do not suffer less because they have no words."
- Anna Sewell (1820-1878)