Hi
I went with my husband to FL on M1 and M2 visas. The simple fact that he was on a JAA type course seemed to be enough. When they interviewed us, we just were truthful, said what our plans were and that was that.
We had to prove we had enough money to live on while there and also have all the million and one forms.
Sorry not to be any more specific, but we literally had nothing else to show them either.
This makes no sense now - I'm sure I replied to a question about evidence of returning to the uk!