Almost 50,000 more pupils across the South West are being taught in good or outstanding schools compared to last year, according to Ofsted's first ever report on education standards in the region.
Despite the improving picture from the 2012-13 annual report, inspectors said too many children and young people from poorer backgrounds were being "let down".
It said pass rates, in junior years and at GCSE, for the 152,870 pupils in the region eligible for free school meals, were well adrift of the national average.
In some cases, pupils on free school meals in otherwise high-performing schools, often serving more advantaged areas, did far worse than similar pupils in schools with a high proportion of pupils entitled to free meals.
Bradley Simmons, acting regional director for the South West, said: "Thanks to the hard work and determination of teachers and leaders over 48,000 more pupils in the South West now benefit from a good or outstanding education than 12 months ago.
"This is due to the commitment of teachers and leaders across the region who, for the most part, have high expectations of children and understand that only a 'good' standard of education is good enough.
"However, the strong performance overall masks the stark under-performance of children from poorer families. They are being left behind.
"At both primary and secondary school level, these children are being let down. Not a single local authority area met the national average attainment figures for children on free school meals at primary school. At secondary school, the picture is equally poor.
"Tackling the achievement gap between the pupils on free school meals and their more affluent peers is a moral imperative.
"That is why Ofsted inspectors have taken a series of measures to help schools use the pupil premium fund more effectively to raise attainment for children on free school meals. We are determined to close this unacceptable gap."
The report showed of 80 per cent of primary schools in Somerset were rated as "good or outstanding" and 86 per cent in Gloucestershire, compared with 89 per cent in Dorset.
For secondary schools, 67 per cent in Somerset received the same rating and 64 per cent in Gloucestershire compared with 86 per cent in Dorset.
As the regional and national reports were published, Ofsted chief inspector Sir Michael Wilshaw warned schools were suffering from a culture of "casual acceptance" of misbehaviour and poor attitude to education in the classroom.