I'm working on my badges and realized I did not have my "Master of Fire Badge", so I checked to see what fire spell I was missing. The only spell I'm missing is Take Power, so I went to Croaky to get it from him, and he doesn't offer it.
I have my level 48 spell (Fire Dragon), but the Master of ... badges are given when you have ALL of the spells for you school. Since I am missing the "Take Power" spell I cannot get the Master of Fire badge.
It seems I am mistaken. When I first got the Fire Dragon spell I did not have the Master of Fire Badge. I was at the time missing two other spells (Quench and Take Power). I found and got the quench spell, and attempted to get the Take Power spell, but couldn't get it as described previously. However I just looked at my badges again and I do have the Master Of Fire badge.
Still not sure why I can't get the take power spell, but since I rarely use minions this is not too much of an issue for me.