The first report to claim the workload deal is having a positive impact on learning in Wales's schools was published this week.
Various studies into the effect of the 2003 agreement - which was designed to give staff a better work-life balance - have been unable to find evidence of improved educational standards.
But Estyn, the Welsh inspectorate, surveyed schools and found that curriculum provision had improved in about three-quarters of them as a result of curriculum changes and new teaching arrangements. Attendance and behaviour had also improved at about a quarter of the schools, it found.
Under the agreement, which applies in England and Wales, teachers have gained planning, preparation and assessment (PPA) time and spend less time on admin and cover duty.
A cross-party enterprise and learning committee report last month found no evidence that any of these arrangements had improved standards.
However, Estyn, which questioned 40 schools, 10 chairs of governors and drew on data from various inspection reports, said standards had improved in some subjects in more than two-thirds of the schools surveyed.
The schools watchdog said the improvement was largely due to better specialist teaching during PPA time, especially in primary schools. Almost half the sample primaries made creative use of the time to focus on particular curriculum activities where standards needed to be raised. In the best cases, cover staff taught pupils specific subjects, such as ICT, PE, music or art.
Estyn said there was evidence that work had improved in these schools and that more pupils were achieving the expected grades in teacher assessments as a result.
The report found that all teachers - no matter what size their school or what phase they worked in - said they felt the benefits of changes linked to the agreement.
But, as has been widely reported, heads and senior staff had seen their workload rise significantly under the agreement. A quarter of primary heads had no dedicated headship time because of the demands of the job, Estyn found.
One of the main concerns was funding. Some schools said they did not have the resources to implement some parts of the agreement. Only six out of 10 schools felt they received enough resources to support teachers' PPA time fully, and two-thirds felt they lacked the cash to provide dedicated headship time.
Many schools said they did not receive enough support or guidance from their local education authority. In seven authorities, support was rated poor or very poor by more than 10 per cent of schools.
Estyn called on the Assembly government to review funding for the workload deal so that schools could implement the changes fully, and urged it to continue to monitor the impact on pupils.
Jane Hutt, the education minister, has already promised an inquiry into how many hours heads and teachers spend covering lessons following the enterprise and learning committee's findings last month.
The committee made 11 wide-ranging recommendations, all of which were accepted, or accepted in principle, by Ms Hutt. She told Assembly members that both reports would influence government policy.
A spokesperson for the Assembly government said: "We are pleased with the over-arching finding that the national agreement is having a positive effect in schools and that, increasingly, schools are examining the link between workforce deployment and educational standards.
"We believe that the full engagement of all schools in workforce remodelling will be key to transforming educational standards."