The only way to speed up a tama's growth is to debug, which is very risky. However, except on Tamatalk, I don't think I know a single failed debug at school, out of twelve tries. I have two warnings:
DO NOT Debug a V4, or V4.5. Unlike the other versions, it's impossible to stop it's fast-forward, and therefore a broken tama.
If you debug your tama, don't Undebug it. This is how my Snakeskin V3 broke.
Also, debugging a V3 causes you to lose the flag game in the Games Menu. It's still there but you can't play.