Exploring my mind

This was sort of a long awaited dream. I just wanted to see if human anatomy works well in dreams. However this dream did not help me in this task.

I was in a room which looked like a classroom. In it there were many people of the "Jiu-Jitsu"-club I once belonged to(in rl). Them were from the second group in which I was at this time. There were also many people I did not know and some friends of mine. This meeting was for all members and interested people. So I could go there too although I was not a member anymore. The trainer who was there was happy to see me and I had to do some techniques too. He also gave me tips of things I didn't know(I even tried them before writing and they work!).
Suddendly someone knocked one the door and group three came in.(The trainers wanted to put me there in rl but they never did in the end) This group was more skilled and there were more older people like in their 20s or even 30s. There were just a few younger people in this group like the girl who gave me the tip in the dream "Strange happenings". She did not do something special in this dream.