He left the pound;8,175-per-year St Martin's school in Northwood, Middlesex, to join Watford grammar school for boys last year.
For music lecturers David and Yuko Vinden the decision was based on a comparison of the secondary, where 95 per cent of Year 11 pupils last year achieved five or more good GCSEs, with some Middlesex private schools.
"It had more to offer, including a much more rounded education in a socially and ethnically-mixed setting," said Mr Vinden, who had painful memories of his former private-school days at the now-closed Truro cathedral school in Cornwall.
A further priority for the family was to find a school with excellent music facilities. Theo scored the joint-highest mark in the county in his grade seven cello exam. Watford grammar selects 10 per cent of its pupils on musical aptitude. Money was not a major factor in their decision, said Mr Vinden.
Meanwhile, Roz and George Lyall were so impressed with the private school they had sent their eldest son George to from a state primary, his brothers also joined him a year later. This academic year will cost them pound;17,202 in fees at Dame Allan's boys' school in Newcastle upon Tyne.
All three attended St Charles' Roman Catholic primary in the city, but Mr and Mrs Lyall feared George, now 15, would have struggled in a large state secondary school.
"We thought he would get lost in the crowd," said Mrs Lyall, a nurse, from Newcastle. Robert, 13, joined the private school at the end of his primary education. David, 11, the youngest son, joined three years before he was due to finish at the state school because his parents were concerned his class of 34 was too large.