The benefits of the increase in school support staff in England and Wales could be hampered by a lack of organisation, a government report says.
Some 100,000 more support staff work in schools than in 1997
The number of teaching assistants and support staff grew significantly between 2004 and 2006, the study found.
And by 2006 most tasks deemed unsuitable for teachers were being done by support staff, which had a positive impact on teachers' job satisfaction.
But many teachers lacked time to plan how they would work with support staff.
The report, commissioned by the Department for Children, Schools and Families, said this meant "the impact of teachers and support staff on pupils may well be compromised".
School support staff range from those supporting pupils with special needs to information and communication technology workers and caterers.
The Institute of Education team sent questionnaires to 10,000 schools, with about 2,000 primary, secondary and special schools responding.
It found that in 2004, the majority of teachers had no allocated planning or feedback time with the support staff in their classroom - with more secondary schools lacking planning time.
By 2006, although communication between teachers and support staff had increased, it had not happened in secondary schools, it added.
It also found three-quarters of the teachers it questioned had not been trained to work with support staff - either in the classroom or as line managers.
The government boosted the range and number of support staff in schools in 2003 as part of plans to cut unnecessary bureaucracy and paperwork and to raise standards.
"From a teacher's perspective, school life is now heavily connected to the presence of support staff," the report said.
It does not look at how pupil standards have been affected by their introduction but instead focuses on the impact they have had on teachers' jobs.
About half of teachers said they had seen a decrease in their workload as a result.
Two thirds said it had made a positive impact on their job satisfaction and reduced stressed levels.
There remains a problem with recruitment with 36% of schools saying they had difficulties and 12% with turnover.
Earlier studies have shown problems arising from a lack of clarity of support staff roles - with few having job descriptions and staff appraisals.
By 2006 fewer support staff (33%) were being supervised by teachers than they were in 2004 (43%).
And two thirds of staff worked extra unpaid hours - with most doing three or more a week.
The study found high rates of satisfaction among support staff, with 79% saying they were very or fairly satisfied with their conditions of employment.
They were less happy with pay levels - half were satisfied but a third were not.
Support staff pay ranges from around £7 an hour for pupil support staff and above £11 an hour for welfare and administrative staff.
Schools minister Jim Knight said the report highlighted the striking contribution support staff make to the effective running of our schools.
"There are 100,000 more full-time equivalent teaching assistants in our schools since 1997, and they are playing an important role in supporting teachers and helping them to deliver more personalised learning.
"It is important too that teachers are trained to collaborate more effectively with support staff.
"The new Initial Teacher Training and professional standards, along with other continuous professional development opportunities, will help to achieve this."