Three-quarters of the schools were "broadly satisfied" with the inspection process, but there were worries about the stress of the long lead-in time, a "snapshot" view of the school, and a lack of advice on how to take things forward.
Despite initial doubts about their value, more than half of headteachers commented on the effective contributions made by lay inspectors. In particular, their ability to ask unexpected questions and good interpersonal skills were noticed.
While two-thirds of heads and more than three-quarters of governors were satisfied with the overall quality of inspectors' judgments, there were more doubts about the judgments on specific subjects. Nearly half of heads and teachers had concerns, pointing to an unevenness in quality, generalisations made on limited evidence, and an over-emphasis on weaknesses at the expense of strengths.
"It may be that the current inspection framework requires more judgments than can be made soundly in the time available," say the report's external validators, Professor Michael Barber and Paul Fuller.
"In our view, particularly in a primary context, where the inspectors believe they have insufficient evidence to reach a firm conclusion they should say so."
"Although schools generally maintain that teaching and learning receive less attention than other areas during the preparation stage, many headteachers report that the greatest value of the inspection for the school was the process of self-review carried out during the pre-inspection period," say HMI.
However, in their commentary, Barber and Fuller warn that in some cases, the long run-up can lead to "an excessive emphasis on the preparation of written policies and documents at the expense of a focus on what really matters, the quality of teaching and learning."
Sixty per cent of teachers were happy about the inspectors' qualifications, and another 24 per cent were satisfied, but with some concerns.
Barber and Fuller comment that "the quality of feedback from inspectors to schools is likely to be an important determinant of whether inspection is followed by improvement". Oral feedback needed to be well-structured and allow time for discussion. Written reports needed to be clear and accessible to a variety of audiences.