The biggest mistake I ever made was to assume I could take to a new senior post all the hard-won good relationships with children I had made in my previous job.
For six years I taught general subjects to "difficult" groups in a highly streamed, high-achieving comprehensive. I established a comfortable relationship with the pupils I thought of as belonging to me. We joked and had some hilarious drama lessons together. I could even take groups out in the minibus with just me, the driver, supervising.
Then, on the strength of my record, I went to a more senior post in another urban comprehensive. Because I was good with problem classes I was given (on top of my management responsibilities, of course) a bottom stream Year 9 group for virtually the whole of their core timetable.
I wasted no time getting it wrong. On day one I blindly failed to take in why the class had been seated in carefully separated individual desks, and I invited them to come forward (it was a small class, in a large room) and sit around a big table so we could chat informally. From then it was all downhill. This was a school where iron discipline was the only quality pupils respected. Teachers were "hard" or "soft" - boy, had I let them know which category I was in.
I never really won that class back - even now I squirm at the memory of what it was like to be in a senior management position and having visible difficulty with one of my classes.
The lessons? First, the age-old one that you start by being a little distant, formal and efficient. Second, that you pay attention to established procedures in your new school. Third, that however senior you are, to the kids you're just another new teacher, and fourth, that you must never be too proud to ask for help.