Simal Patel is moving on from the south London school where she taught to become an NHS trainee manager in Nottingham.
But she leaves with great respect for her former colleagues at Aylwin girls' school, Bermondsey.
"I want to try something else before I commit. I know how much teachers have to put up with now, especially in challenging schools," she said.
Miss Patel, 23, originally from Nuneaton, who read biochemistry and pharmacology at King's college, London, said she had really struggled with teaching when she first entered a classroom. But by the second year of her time at Aylwin girls', she had earned respect as a science teacher.
She said: "The first three or four months were really tough. I had to stick it out to build up respect before the lesson would go to plan. The children did not know if I was there to stay and I felt I was failing them as a teacher.
"I went in with high expectations of what I could achieve and then there was the shock of going in when I realised I couldn't get the kids to sit down yet. It was sink or swim at first."
Miss Patel said that although she was given six weeks training, the lack of practical experience meant she had to learn fast in the classroom.
She said: "If you had asked me if going in cold was a good idea last year, I would have said no. But looking back, I developed quickly and it made me very pro-active and a really strong person."