I agree, a 10 gallon isn't really big enough for a school of them. I wouldn't personally put them in any tank smaller than 30 inches long or so. They're extremely active, especially when they're young. Although you could physically fit a small school in a 10 gallon, and the tank could support them, they really wouldn't have enough physical space.
If you manage to get your hands on a bigger tank, I suggest platies. They're active, colorful, and peaceful. Unless you want babies, though (since they're livebearers), I suggest that you get all males. You could easily fit 6 in a 20 gallon, plus 6-8 danios, with space left over.
Current bettas: ♂Opalo, ♂Granite, ♂Alpha-Betta, ♂Eclipse, ♂Lucky, ♂Honor, ♀Virtue, ♀Innocence, ♀Garnet, ♀Chroma, ♀Tethys, ♀Amaryllis, ♀Goldeen
Tanks: 3g betta NPT, 20g NPT community, 10g 3-way divided, 10g NPT sorority, 5g divided betta tank