The project has been organised by What Works for Children's Social Care, in association with its research partners at the Children's Social Care Research and Development Centre (Cascade), Cardiff University.
An interim report on the scheme's success says it is "showing early signs of improving inter-agency working and building more collaborative relationships with children, young people and families".
The schools involved are in Lambeth, Stockport and Southampton and the project is said to have gone down well with both school staff and social workers.
A statement from the organisation says: "Greater familiarity and more regular contact between social workers and school staff has created a better understanding of the different contexts in which the two groups operate and the challenges they are facing.
"School staff appear to value having timely and relatively unrestricted access to social workers to act as a sounding board and reassure them that they are taking the appropriate action."
The interim report also suggested that the pilot is helping relationships between social workers and the children and families they support. This seems to be because their regular presence demystifies social care.
Social workers are also seeing an impact with parents. One social worker reported that being visible at assemblies, in the playground and dropping-off and collecting time was helping to build a familiarity with parents.
One of the head teachers involved said that having social workers in schools would do a lot to "prevent the image of social workers as child snatchers".
The interim report did note that there had been some challenges, notably in cultural differences on approaches to discipline, but also in practical matters such as IT access and data sharing.
However, school staff and social workers in all three local authorities involved were mostly positive about the pilot with staff in some schools now interested in having a permanent dedicated social worker for their school.
Michael Sanders, executive director of What Works for Children's Social Care, said: "This is our first major project at WW-CSC, and it's exciting to see results begin to come in - and show so much promise.
"We'll be following up early next year to see if the potential impacts are being realised, but for now, the indications are very positive."
Chris McLoughlin, director of children's services at Stockport Metropolitan Borough Council, said: "This collaboration is making a very positive contribution to our learning and to the overall development of the programme.
"Although relatively early days, we are already seeing a significant impact in terms of our ability to respond more swiftly and effectively to the needs of our children and families.
"Locating social workers in schools is showing real benefits in promoting collaboration, building stronger and more productive working relationships and ultimately improving the social care and early help offer within the community.
"We are very encouraged by the early findings."