I was never a fan of school; I struggled academically and I was bullied. Also, I was always in the shadow of my brother Richard, who was a year older and very intellectual.
At Ogmore Comprehensive School (in the Welsh valleys), the only teacher who didn't constantly tell me I wasn't as good as Richard was Mr John, who taught PE. It was the only subject I shone at. As well as rugby, I played football, cricket, tennis, squash and table tennis. I did athletics, too. Sport made me feel alive.
Mr John always had time for me. He made me feel that what I did was worthwhile, and that if I stuck at it I could be successful. He knew that I wanted to make a career out of sport and he encouraged me. He also tried to talk me out of bunking off. He would say: "Don't skip school because you're not excelling at the academic subjects, keep coming because you are excelling at sports."
But the work wasn't the only reason I disliked school. I was also being picked on by my rugby teammates. When we went swimming, they would smack me with their wet towels. I got spat on, too. It was degrading, but I didn't want to tell anyone because these were my rugby mates and I wanted to be in the team.
I'm not sure why it happened, I wasn't small or weak. I think it was because I didn't stand up for myself. It started with a little thing - I was probably singled out because my rugby boots weren't the best - and then it built. Going to school eventually became a nightmare.
One day, when I was about 12, I started crying and told my mum everything. She marched up to the school and sat down with the headteacher. Nothing was ever said to me, but the bullying stopped and life got easier. I'm still in touch with loads of those old rugby mates now.
So my early teenage years weren't that great. And later, when puberty kicked in, I began wrestling with my sexuality. I would watch the other boys to see who the right girls were to look at. Even though they weren't of much interest to me, I couldn't let anyone know.
Mr John was the only positive throughout my school years. He massively encouraged me. He told me to stick to my dreams and to work as hard as I could to achieve them; his words have stayed with me.
I didn't sit my GCSEs as I knew I would fail them. My mum said I could leave school if I got a job, so I worked in a factory, lifting metal to make filters for cars. It was the hardest job I ever had and a wake-up call.
Then I got scouted to play rugby professionally. When I first started playing for Bridgend, Mr John used to come and watch. It was quite surreal: we'd meet in the supporters' lounge and I would try to have an adult conversation with someone I had connected with as a child.
He never stopped telling me how proud he was and that he had always known I would make a success of myself. He was a real inspiration, but unfortunately we lost touch when I moved from Bridgend.
Teachers have such an overwhelming power over how you feel about school. If not for Mr John, I'd have spent half my time bunking off - I knew I couldn't compete with my brother's knowledge. I just wish the other teachers had judged me on my ability, like Mr John did.
Gareth Thomas was talking to Kate Bohdanowicz. He is leading an anti-bullying campaign called Balls to Bullying. For more information, visit www.prosperoteaching.com
In the scrum
Born 25 July 1974, Sarn, near Bridgend, Wales
Education Ogmore Comprehensive School, Bridgend
Career Retired Welsh national rugby player and captain; made 100 test match appearances