The Paisley University study of the SQH, a two to three-year training programme aimed at aspiring heads, concluded: "The overall findings of this study are extremely positive and confirm the significance of the SQH programme for the future of Scotland's schools."
But Danny Murphy, head of the Centre for Educational Leadership at Edinburgh University, who will leave shortly to go back to being a school head, commented: "While these positive findings show that systematic and structured professional development can have a desirable impact on practice, the successes should not blind us to the need for further improvement."
The five-year-old qualification has been backed by pound;4 million from the Scottish Executive but funding beyond 2005 is in doubt. From that year it (and any other programme that might be developed) will have to meet the national Standard for Headship which will become compulsory for all new heads.
Mr Murphy says SQH training has been most successful where those taking part are supported by their schools and authorities. "Yet it is precisely the people in the most difficult and challenging work environments who need the greatest support to develop," he comments.
He also urges the Executive to extend the opportunities available from the SQH to other managers for whom there is a lack of structured training.
The future of the SQH is about to be reviewed by the Executive and Mr Murphy suggests that a new approach must fit "more seamlessly into a progressive menu of high-quality professional development in leadership and management, supporting those at all stages of career".
The evaluation notes that individuals have benefited largely in the improvement of leadership and management skills, while the strongest gain for schools has been in better learning and teaching. Graduates believe that the SQH experience has enabled them to implement change and improve team-working.
They are less certain about whether a better trained management has fed through into improved pupil attainment. "Those whom we interviewed felt this crucial measure could only be properly judged when a longer period of time had elapsed from completion of the programme," the report states.
The one part of SQH which did not receive a positive health message was the accelerated route which can be completed in as little as eight to 11 months. The pressures that this imposes on individuals are such that "it is not functioning as a development programme for the candidate nor is it having a significant impact on the candidates' schools".
Mr Murphy acknowledges that the programme in general "has an intensive impact on the work-life balance for mid-career professionals who are often already at full stretch in trying to meet their different work and home demands".