Alan Barber, 59, former head of maths at East Bridgwater community school won pound;72,547 when the House of Lords agreed his managers should have taken his concerns more seriously.
Mr Barber won his original claim for compensation, but this was overturned by the Court of Appeal. This month, the House of Lords quashed the appeal court decision.
Mr Barber joined the school in 1984. By the mid-1990s the school's pupil numbers had halved and the management team was restructured.
He was demoted to the post of maths co-ordinator, lost the support of two part-time deputies and was then given extra responsibility as the school's publicity officer in order to regain his previous pay.
He took three weeks off with depression in May 1996. When he returned to work in the summer term he told three senior managers that he was not coping. But nothing was done to relieve his workload and in November 1997 he went off sick once more. He was granted ill-health early retirement four months later.
Mr Barber said: "I felt pretty exasperated, if not a little desperate."
In his judgement Lord Walker of Gestingthorpe said: "Even a small reduction in his duties coupled with the feeling that senior management was on his side, might by itself have made a real difference."
Mr Barber, who is divorced with three adult children, said: "Until there are a lot of serious improvements in teaching I fear I could not recommend it to my children, which I feel very sad about."