He co-wrote the book Middle Schools, in 1975 and travelled the globe giving lectures on the subject.
He believed passionately in the special educational requirements of pre-adolescents and the need for a specific type of school for them.
Mr Gannon's family say he was a great advocate of learning through the enjoyment of creative, expressive activities such as writing and crafts.
He rejected testing regimes, the 11-Plus exam and rote learning, believing all children should have the same opportunities.
His son John said Mr Gannon would have been very disappointed about the gradual disappearance of middle schools, which numbered 1,500 when he retired in 1980. Today there are 345, many of them under threat.
Mr Gannon's teaching career did not start until after the Second World War, during which he sustained a serious head wound. He taught modern languages in East Sussex and Yorkshire before being appointed first the head of Milefield school in Grimethorpe, South Yorkshire, the first purpose-built middle school. As a result of its success he was awarded an OBE in 1974 and was invited by the BBC schools council to become a spokesman for the three-tier school system in countries as far flung as Japan.
After he retired, he taught children with special educational needs at the private Newlands school in East Sussex, which named its learning support centre after him.
His son John said: "He was very proud to be part of the middle school movement."
Mr Gannon leaves a widow, Peggy, 84, and three sons.