I arrived at Fishguard Comprehensive in Pembrokeshire at the beginning of the upper sixth. I came from a school that I don't want to name as I don't want to give it any promotion.
Martin Bradley taught A-level French. I had already studied a year of sciences, but I'd decided to switch to languages so I asked if I could join his class. He was hesitant. Even though I had French O-level and was singing songs in French, he was doubtful that I could complete a two-year course in half the time. Nevertheless he accepted me, and I respected him for that.
The first lesson he taught me was not to judge someone as soon as you meet them. He was quite cold to begin with and, as I was strident and a little contrary, I wasn't sure we'd get on. But then I started going to his lessons and realised that we got on great guns. Now, if I don't automatically click with someone, I can be sure that somewhere down the line they might become one of my favourite people.
I loved Mr Bradley's classes. He didn't patronise his pupils in the way he spoke to us or in terms of content. He had a dry sense of humour, which he never compromised to be popular or to entertain us. He introduced me to French literature such as Thrse Desqueyroux by Franois Mauriac. That book had such an impact on me; there's a nod to it in one of the first songs I wrote for Catatonia. It was called Difrycheulyd, which means immaculate.
Mr Bradley taught me to have a 360-degree view of the world. I grew up in Welsh-language education and watched Welsh-language television, so I was interested in the protection of minority languages. He had arrived from somewhere in England and he asked me why there should be Welsh-language TV if it alienated non-Welsh speakers.
I hadn't thought of it in that way and a light bulb went on in terms of being able to look at an argument from someone else's point of view. I didn't agree with him, of course. If you move into an area, you should learn the language and then you can watch the TV. We had an interesting conversation about it.
It was important for me to see another side of an argument as I'd always questioned anything I thought was unfair or illogical. I would never tolerate bullies, for example. At primary school I campaigned for girls to do woodwork alongside boys - we had to do sewing and I thought it should be up to the child to choose. My protests didn't change anything at the time, but maybe it was part of a growing wave of looking at the gender division in schools.
I got a B in my French A-level, so Mr Bradley taught me another lesson - the enjoyment of proving someone wrong. He was over the moon when I went to study French, Welsh and Spanish at university. I only stayed a year, though, as I left to make it in the music business. I'd never studied music or told my teachers about my ambitions. I taught myself guitar and songwriting and I didn't need anyone to help me out. I needed to find my own way.
Mr Bradley was the first teacher to treat me like an adult. He allowed me to grow up. He was one of those inspirational teachers who dedicate their lives to sharing their knowledge and get little recognition for it. I'm very grateful to him.
Cerys Matthews was talking to Kate Bohdanowicz. She co-founded the Good Life Experience festival, which takes place on 18-20 September at Hawarden Estate in Flintshire. Tickets are pound;45. www.thegoodlifeexperience.co.uk
The best days
Born 11 April 1969, Cardiff, Wales
Education Fishguard Comprehensive, Pembrokeshire; Cardiff University
Career Singer and songwriter, author, and broadcaster on BBC Radio 6