An unprecedented number of schools judged to be 'inadequate' in the last year has triggered a slump in the overall rating for Norfolk children's services.

Ofsted gave 15 of the county's schools - 10 primaries and five secondaries - the tag in 2009/10, which was the highest number of any of England's 152 local authorities. Last year, two primary schools and three secondaries were judged inadequate.

The issue was one of the key factors in pushing Norfolk's Ofsted annual performance assessment grade down from level three (performs well) in 2009 to level two (performs adequately) this year.

In a mixed report, inspectors praised the council's support for the most vulnerable children, and said a 'large majority of all types of services, settings and institutions' were good or better.

But they picked out a host of shortcomings, including:

? The attainment of very young children is 'static and lower than in similar areas'

? Not enough 11-year-olds are making sufficient progress in English and maths

? Not enough 17-year-olds continue with their education or training and "too few" 19-year-olds are obtaining qualifications

? The proportion of statements of special educational needs that are produced on time is "well below average"

? Pupils are "not making sufficient progress in one in four secondary schools

? Attendance in secondary schools is improving, but remains "much lower" than in similar areas.

Ofsted said the council had 'strengths in its services and provision for children and young people whose circumstances have made them vulnerable, such as those in care or with special educational needs'.

Other praise for support to vulnerable groups included:

? Children in need of protection are consistently responded to in a timely and assured way

? The virtual school has been instrumental in helping children in care achieve more

? Most recent data on teenage pregnancy shows a fall at a higher rate than in similar areas and nationally

? Parents of disabled children indicate their levels of satisfaction with local services are much higher than average

? A high proportion of special schools and children's homes are outstanding and almost all of the others are good

? The local fostering agency is good and the local adoption agency is outstanding.

Lisa Christensen, director of children's services for Norfolk County Council, said: ' A large majority of our services are good or outstanding and we are responding to children in need effectively – this is a key priority and an area where we must maintain our focus.

'We are pleased that Ofsted has praised our support to the most vulnerable children and young people, including those in care, those with special educational needs and those with disabilities. These are the children that need our help the most and it is important that they are able to access the support they need.'

She added: 'Our performance has improved in many areas in the last year but we have seen an increase in the number of inadequate schools in the county. This is a source of disappointment and has had an impact on the overall pace of improvement. 'The majority of our educational attainment indicators are in line with similar areas. Our overall performance is deemed as adequate but we are determined it will improve. Ofsted has said our support to struggling schools is good and we are hopeful that new academies in Thetford, King's Lynn and Costessey will help to have an impact on overall results.'

Alison Thomas, cabinet member for children's services, said: 'There are many positives to draw from this report, particularly the support we provide to the most vulnerable and most in need. Our social work has been praised and child protection continues to be our foremost priority.

'Educational performance is adequate but we want it to be good or better. We know what needs to be done to improve further and are absolutely committed to continuing our determined pressure to drive out poor performance.

'This includes working very closely with schools that have a notice to improve or are in special measures. We have had much success in recent years in removing schools from these categories but we will not be satisfied until all our schools are good or outstanding.'

? To read the full report, visit www.ofsted.gov.uk.