Schools have used workload reforms to improve teachers' lives but not necessarily to improve education, the inspectorate Ofsted has said.
Teachers felt better able to focus on the job in hand, Ofsted said
Ofsted said the deal between government and unions was meant to raise standards as well as to reduce workloads.
It said schools in England had tended to treat the improvement to teachers' work/life balance and the greater use of support staff as ends in themselves.
They "believed strongly" standards were rising, but had little firm evidence.
The deal struck in 2003 set out a seven-point plan, to be implemented over three years, to reduce teachers' workloads and improve standards, Ofsted said.
Essentially this involved delegating many routine tasks to support staff, then guaranteeing teachers half a day a week out of the classroom for planning, preparation and assessment.
Ofsted inspectors visited 51 primary schools, three special schools and 45 secondary schools in inner city, suburban and rural locations between September 2005 and March this year.
Ofsted said: "The survey that formed the basis for this report found that the reforms have resulted in a revolutionary shift in workforce culture, with clear benefits for many schools."
Teachers were focused more directly on teaching and learning.
Head teachers and senior managers "continued to sustain a heavy workload", but increasingly with the support of outside managers.
"The substantial expansion of the wider workforce at all levels is allowing the survey schools to extend the curriculum, provide more care, guidance and support for pupils, and use data more effectively to monitor pupils' progress."
Many of the schools saw significant benefits.
"However, as most of the schools did not monitor and evaluate the impact of the reforms on pupils' learning, they had little firm evidence to show whether standards were rising as a result."
Ofsted recommended that the Department for Children, Schools and Families should help schools and local authorities "to understand and prioritise its national agendas for school improvement".
The Training and Development Agency for Schools (TDA) should help them to manage the performance and career development of the expanded workforce.
Its chief executive, Graham Holley, said it must "continue to support schools to make the most of the mix of talents and skills their whole workforce has to offer".
Ofsted said schools should monitor and evaluate the reforms, agree working practices for support staff and share good ideas.
Schools Minister Jim Knight said there were 36,000 more teachers and more than 100,000 additional teaching assistants compared with 1997.
"Great strides have been taken ... but there is more work to do.
"We will continue to work with unions, heads and the TDA, to make sure all schools shape their working practices to deliver maximum benefit to pupils and the whole school workforce."
The classroom union that has been most in favour of the "social partnership" with the government, the NASUWT, criticised Ofsted's report.
General secretary Chris Keates said: "To draw conclusions on the basis of contact with 100 schools out of 23,000 is risible.
"Despite the favourable assessment of schools' progress given in today's report, the NASUWT will continue to question the contribution and value to the education service of Ofsted reporting."
Martin Johnson, of the Association of Teachers and Lecturers, said it was pleased Ofsted had confirmed the social partnership was improving the working lives of school staff and the performance of pupils.
"However, we know much still needs to be done, in particular to reduce the workload of school leaders, improve access to continuing professional development, and further cut teachers' workloads.
"We will keep up the pressure to ensure these issues are tackled."