Betta's come from rice patties in south asia, there is a reason that they are kept in cups at the lfs...They do not REQUIRE heat to thrive.
First, they are not kept in cups because they don't need heat, they're kept in cups because they can breathe air, therefore don't need dissolved o2 that would be provided in a filtered tank.
Second of all, surviving in a cup at a store doesn't reflect their necessary long term housing since many fish will survive in inadequate conditions for a short amount of time.
You cannot compare the temperature needs of captive bettas, which have been bred in temperature controlled tanks for years and years to wild bettas.
Captive Betta splendens are generally bred in tropical environments and that's what they're used to. They have not been selectively bred to tolerate cold temperatures, and there has not been natural selection, like in the wild, weeding out the weaker ones that will not survive temperature drops.
Breeders that keep their bettas in unheated tanks still tend to keep them in rooms that are fairly warm, or they are bred outside in regions where temperatures do not fall all that far.
Even if wild bettas can tolerate lower than tropical temperatures, it does not mean that they can tolerate temperature drops that would be present in a 10g tank in an unheated class room in a northern region of the U.S.
The OP is in New Jersey and it gets frigidly cold there.
I don't see a betta handling below 60 degree temps for very long, if at all.
This is all a moot point in regards to the OP though, because they seem to know better than to keep a betta in the conditions they've described for this classroom.
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