Many schools are failing to provide teaching assistants and other non-teaching staff with sufficient support to enable them to help to raise standards in the classroom, a report by Ofsted has said.
Only six of 30 secondaries, primaries and nurseries studied were found to be using the roles effectively or providing adequate training and professional support.
In the worst six schools, the report said support staff "did not always understand how their work related to that of other staff across the school and how they could make a difference to pupils' learning".
It also claimed there was "huge variation" in the levels of knowledge, expertise and ability of support staff and "the capacity of leaders and teachers to provide meaningful direction for their work".
It said this situation led to support staff being either overstretched or having their skills underused.
The report said that schools needed to be clear about each member of staff's responsibilities for improving teaching and learning.
It also advocated more monitoring of the specific contributions made by members of non-teaching staff.
The Training and Development Agency for Schools, the report said, should help to provide better information and guidance on the national occupational standards for support staff and the career development framework.
The report called for the Department for Children, Schools and Families to provide more guidance on appropriate levels of pay for the "increasingly diverse roles" that had been introduced.
Ofsted chief inspector Christine Gilbert said: "The effectiveness of the workforce reforms put in place in 2003 depends on all school staff being valued and treated as professionals.