More students are seeking help from counsellors and guidance services - and a report has found many school services are struggling under pressure or simply not up to scratch.

The Education Review Office has raised concerns about the quality of secondary school guidance and counselling services, and says improvement is needed at about one school in three.

It has asked the Ministry of Education to review funding, as it could be restricting the number of guidance workers at schools with large rolls.

Other schools were unable to account for how they spent money provided for guidance staffing.

"Many schools undertook little or no self-review of their guidance and counselling provision, so school leaders didn't know if it was meeting the needs of students," said Stephanie Greaney, evaluation services manager for ERO.

"Student wellbeing is critical for student achievement ... we found that the varying importance which schools and wharekura placed on the role of guidance and counselling contributed to the variable quality of service we saw provided."

The report, Improving Guidance and Counselling for Students in Secondary Schools, is part of the Prime Minister's Youth Mental Health Project, which aims to improve the mental health of people aged 12 to 19.

Its findings are based on visits by the ERO to 49 secondary schools and wharekura this year. A survey of 671 students at the schools was also done.

Mrs Greaney said a key finding was an increasing workload at many of the schools made it difficult for otherwise competent staff to help students.

Just over one-third of schools surveyed needed to improve the guidance and counselling offered.

As well as a funding review, the ERO has recommended the ministry provide clear guidance and support, including professional learning and development for school leaders and guidance and counselling staff.