Background: In the UK an estimated one in ten primary school pupils have diagnosable mental health problems which may impact their education. Aims/context: This study examined a primary-school-based art therapy service for children experiencing social, emotional and mental health difficulties to assess the intervention's acceptability and possible changes in classroom learning. Methods: A mixed methods before-and-after study was conducted with 25 children in art therapy and a comparison group of 25 children per subject for reading, writing and maths attainment. A focus group with 10 teachers and interviews with 37 children were used to examine perceptions of art therapy and classroom learning. Results: Academic attainment was similar between the art therapy and comparison children. Both groups' learning rate resembled that of national minimum expectations. Children and teachers perceived art therapy to be helpful for engagement with classroom learning, relationships with teachers and peers, and learning time. Conclusions: Further research is needed to develop this primary-school-based art therapy programme, assess transferability, and examine wider educational outcomes. Implications for practice: Primary-school-based art therapy may be particularly helpful when it is perceived as: a safe place, sessions being social and fun, facilitates coping strategies, expressing, thinking and talking, as well as making artwork. Plain-language summary In the UK an estimated one in ten primary school pupils suffer from mental health problems, and this can affect their educational attainment. Thus, it is important that therapies help children to gain positive outcomes both in mental health and educationally. We looked at one art therapy service, which specifically focuses on helping children to understand their own and others' minds (metallization), within one primary school in London. Thirty-seven children referred to art therapy with social, emotional and mental health difficulties were included. Ten class teachers participated. The aims were to see if the children, and their teachers, found the approach acceptable and if there were any indications of changes in classroom learning. There were no differences in reading, writing and maths scores between children attending art therapy and comparison children receiving usual education support. However, all the children learned at the same rate as the national minimum expectation. Art therapy may have prevented the increasing educational attainment gap that social, emotional and mental health difficulties can bring. We held a focus group with the class teachers and interviewed the children and both reported experiencing art therapy as helpful for engagement with classroom learning, relationships with teachers and peers, and learning time. Specific aspects of art therapy which they considered helpful were: art therapy being a safe place; learning coping strategies; expressing, thinking and talking in art therapy; making artwork; and sessions being social and fun. The teachers also a...