With learning support staff an increasing part of the school workforce that is assuming more and more teaching related responsibilities, attention has grown as to how their skills and practices can have the greatest impact on students. “Learning support staff” are defined as those school staff whose main function is to assist the work of teachers. This paper reviews country approaches to the roles and responsibilities of learning support staff. It discusses the different mechanisms through which learning support staff can have an impact on teachers’ work and student achievement and reviews the related empirical evidence. While the available research provides mixed evidence on the impact of learning support staff on student achievement, it suggests that learning support staff may improve teaching and learning as long as adequate strategies for their training, deployment and use are implemented. There are several ways through which learning support staff may have a positive impact on student attainment. Students receive more individualised help and attention from either the support staff or the teacher; and the learning environment can be made more flexible possibly leading to increased engagement and inclusion of children in classroom activities. Also, teachers receive specialist support and assistance with their administrative and planning tasks, granting them more time for their core responsibilities.