IO540,
That is totally horrendous. It's none of their business who you fly with!!!
I don't know what you can do about that really. Would just having a chat to them do any good....explaining that people who learn more about flying get more confident and do more flying, which will mean more money in their pockets? More pilots who fly for longer helps the schools too - more self-fly hire, more sales in cafes etc, more landing fees - we should all be on the same side really. You argue pretty convincingly on PPRuNe; can't you convince the school in the same way?