On my first day at school I thought the milk smelt funny and I would not drink it so I was kept in during break. I remember not liking that teacher at all. Despite that I was good in primary school. I enjoyed the work, and when I was about 7 there was a group of us who asked for homework even though the teacher said we wouldn’t get any for two years. I remember racing through the sums to get them all done.

I passed my 11-plus but we moved to Bolton and I went to secondary school. It was a disaster. I was in 2B, 3C, 4D, 5E, lower 5E. They didn’t have a 5F.

Bolton was a bleak and dirty industrial town in those days, quite a shock from being brought up in Bristol. I went to Bolton County Grammar School, and on the first day all the kids made a corridor and the first years had to go down it and were hit by satchels. That was the last year they did it.

One day we were ushered into the lecture theatre and in came this deep sea diver whose job it was to clear up all the wreckage in the ports left by the war. He took out a stick of gelignite and told us that it was what he used to clear the wreckage and it was unstable.

He put it on the desk and walked to the blackboard. As he walked, the stick of gelignite rolled down the desk on to the floor and 300 kids dived under their chairs. He picked it up and said: “No, this is wood. Gelignite is dangerous.” That was the most memorable moment in my secondary education. I really didn’t get on, except in maths. A couple of months before I left, Miss Hoyle, the senior mistress who was also the head of maths, was marking my work and she said: “Which one is Ball?” She didn’t know who I was after five years because she only taught the top set.

She said: “Come here” so I went and she said: “Could you explain how you got this result?”

It was algebra and I told her how I’d done it and she said: “You’ve never been taught that.” I said it was obvious and she said: “It might be obvious to you but it isn’t obvious to everybody.” She looked through my book and said: “Ball, do you know you have a quite brilliant mathematical brain?” It didn’t matter whether I had; she told me I had and I believed it.

I left with two O-levels, including maths. I was pretty certain I was good at maths and when I left school I took up mathematics as a hobby. It was 23 years later that I wrote Think of a Number and opened up a whole new career, which is now 30 years ago.

I can’t say that I got on with the teachers all the way through secondary school, and it was terrible that children could fall through the net like that. But Miss Hoyle at least told me I had a mathematical brain

Johnny Ball, 69, presented television programmes including Think of a Number, Think Again and Think Backwards. In 2004 he was named one of the top 40 most eccentric TV presenters of all time. He is supporting Becta’s Next Generation Learning campaign to encourage the use of technology in education. He was talking to Nick Morrison.