GCSE grades at Royston High School slipped last year because of the controversy surrounding the appointment of a headteaching consultant, an Ofsted report has found.

Inspectors visited the school last month for the first time since Kay Jenkins quit as headteacher. She hired Mark Braine to act as consultant, even though at a previous school he had been found guilty of bullying, making unwanted advances to female members of staff and favouritism to his wife and daughter.

She quit in the aftermath of an investigation into his appointment. The school was graded as good overall and the report stated that standards at both key stages had improved faster than the national average.

But it added: "The decline in the proportion gaining higher grade GCESs in 2007 was the result of major changes in leadership and management that led to significant turbulence in the school and the impact of a small number of students with significantly high levels of absence.

"These difficulties have been tackled rigorously and the leadership of the school has stabilised over the last six months. As a result, the school is back on track to achieve its challenging targets." The quality of teaching and learning were found to be good as was the relationship between pupils and teachers.

Personal development and students' behaviour were also good but attendance was graded as satisfactory. The school would not comment on the slip in grades, but acting headteacher, Carole Henshaw, said: "We are very happy with the Ofsted report. It reflects the commitment and hard work from the governors, staff, pupils and parents.

"We now have to continue to work hard and aspire to be outstanding in our next report." The report said the school must improve the use of assessment in all lessons in order to increase the engagement of students and that teachers consistently use the behaviour for learning strategy.