Alexander, 12, attends Holmwood House in Essex, where day fees are Pounds 10,500 a year, while Mrs Roychowdhury teaches art at Sudbury upper, a state secondary in Suffolk.
She said: "It became apparent when Alexander was young that he was a high-ability child, and not a boys' boy. We believed he would thrive in that environment.
"I was afraid he might get bullied. He likes music and sports, particularly squash, which isn't really a game played in state schools.
"Class sizes are also much lower - he is in a class of 11 rather than the 30 I teach - and there is a very strict discipline code."
She said that teachers, like all parents, wanted the best for their children. "You have to look at your child's needs and try to send them to the best possible school.
"We are lucky because Alexander is on a 50-per-cent scholarship, so we pay half the fees. He leaves next year and I hope he will get a scholarship again."
She added: "State teachers do the best they can for pupils. I have high expectations of all my pupils and want them to do as well as children in any school."