Those lessons where everything slots into place and you get a feeling of "lift-off". Interest is generated, content is communicated, the mood is relaxed but intellectual, disciplinary issues disappear, I am excited, and the pupils are following my trains of thought - and each others' - it seems impossible to believe that I am actually being paid for this.
And the worst?
Trying to deal with negative pupils.
What would you be if you weren't a teacher?
Perhaps a musician. I've played violin and guitar since I was a child, and throughout my career I have played with the school orchestra, as well as in chamber groups outside school. I composed a symphony (of sorts) that was performed by the school orchestra and conducted by the headteacher.
What do you like about your school?
A great deal - which is why I have been here for 32 years. The grounds are beautiful to walk around in, and the buildings are attractive. I've enjoyed working with the same wonderful colleagues in the physics department for many years. I like the great cultural and intellectual variety of the pupils. I have also never received excessive pressure from "above".
What's your ambition in teaching?
To have the best possible lessons with my pupils - that was my ambition in 1976 and it still is today.
How's your work-life balance?
Fine, but that's because I don't make the distinction. I don't spend my school day thinking: "Soon it will be time to go home, and start living." I spend my life doing various things - one of which I get paid for.
How have you changed as a teacher?
I have become more sensitive to the fact that many pupils find physics difficult.
Most embarrassing moment?
Hitting a wasp too hard in the middle of a lesson, and breaking the window. Or teaching a lesson with my fly undone. It might have been a nightmare, but I am fairly sure it wasn't.
Philip Thonemann, 58, was talking to Steven Hastings
1976 - present: Physics teacher at Mill Hill School, London.