However, they need better training, especially to support those who have behaviour problems, a report has found.
The study, from academics at University College Northampton, found that teaching assistants were key to making pupils with special needs feel part of a mainstream class.
The most successful assistants were those who had strong relationships with pupils, had good listening skills and worked one-to-one with youngsters.
They were also chosen for qualities such as fairness, patience and tolerance, and being able to use a range of strategies to help those with difficulties.
The report, by Barry Groom and Richard Rose, said: "The role of the assistant has undergone a transformation from the time when classroom assistants were seen as an extra pair of hands in the classroom, to the present day, where they are perceived to have a more professional role.
"A growing number are deployed to work with pupils with social, emotional and behavioural problems, and to play a major role in supporting the teacher in the management of behaviour in the classroom."
The two-year study into the effectiveness of the use of assistants in 90 primary schools in Staffordshire, presented at the Inclusive and Supportive Education Congress in Glasgow, last month, found that schools looked at personal qualities above qualifications and training when recruiting assistants.
Many considered it a high priority to release assistants to attend courses relating to special needs and behaviour.
Schools expected assistants to develop good relationships with pupils, which they considered key to building pupils' self-esteem and confidence.
Assistants were also expected to give children with special needs one-to-one help to forestall the need to take them out of the classroom during group sessions, such as the literacy hour.
Teaching assistants were found to be most effective when treated as full members of staff and consulted over issues such as planning and review.
* Supporting the inclusion of pupils with social, emotional and behavioural difficulties in the primary school: the role of teaching assistants is available from Barry.Groom@northampton.ac.uk