Ballistic ways of teaching maths
But sometimes Alastair Cornish, head of maths at Michaelston community college, in Cardiff, just wants to talk about his sport.
The 38-year-old has been rifle-shooting competitively since the age of 15 when, after two knee operations, he needed to find a sport that did not involve any running. At 17, he became British junior champion. Since then he has held three championship titles and broken two British marksmanship records.
"I'm chuffed when I win, so I subject my A-level students to a lesson in ballistics," he said. "It's Newtonian physics. Then we work out average rifle scores, using mean, median and mode.
"You can definitely relate rifle-shooting to lessons. It's not PC, but the kids like it: they always ask whether I shoot living things. I think they're disappointed when I tell them it's only paper targets."
But, while he is able to combine his two interests in the classroom, Mr Cornish has found his hobby increasingly incompatible with the day job. "I love teaching but I haven't shot really well since entering middle-management. I work 60 hours a week, and I'm shattered."
He has decided to leave Michaelston to work as a supply teacher, so he can devote more time to improving his skill as a marksman. His ultimate aim is to compete in the Commonwealth Games in Melbourne in 2006.
But handing in his notice was not an easy decision, and he is acutely conscious of the shortage of maths teachers. "You always feel guilty when you leave a school. You wonder about the pupils you are leaving behind.
It's harsh, but you've got to do what's best for you. If you want to be a good sportsperson, you've got to allow yourself to be selfish."