Hesperis, puberty changes the voice for both females and males, so what you experienced is normal. Many teachers will not take a child as a voice student until they have gone through the puberty changes, and I think there is good reason for that decision. Charlotte Church, for example, was pushed too far with her voice, too young, in my opinion, and now she sounds like she is losing it. She has lots of tension - her lower jaw shaking up and down when she sings. I hope some day you can get private lessons with a good voice teacher. An affordable way to start would be to contact my teacher by email at the address I posted above.

Amy, thanks for joining the forum. Threads on singing technique have been cropping up over the years. There's a collection I linked together in one thread. Regarding the teacher/coach label, I have used my teacher as a coach when I needed her guidance before specific performances, but I agree, not all coaches are teachers.