Oh gosh, were those the times.
I was 9 years old and my mom FINALLY let me take lessons. It was my first riding lesson on a beautiful appaloosa POA pony, an old one at that. I was on a lead line and the trainer would jog along side at the trot, and I didn't know how to post yet but she exampled the concept to me, had me practice at the walk, and attempt at the trot. I could not do it.
Now at my barn it's VERY favorable to take group lessons, as private lessons are VERY expensive. But they have a rule for beginners- You can't join a group lesson till you learn to post the trot. Well, 6 or 7 private lessons in and I still couldn't get it. My mom said to me at that point, that if I couldn't get it by the next lesson I couldn't take lessons anymore because the private lessons were so expensive. I got it quickly after she told me that, THANK GOD!