In this chapter, the author argues for the importance of a thorough subject knowledge for teachers with an emphasis on understanding the links between concepts and scientific domains. She argues that this knowledge is essential for teachers working with children with special educational needs (SEN), as only through a clear subject understanding can teachers be aware of children's progression in conceptual development and make the links between topics explicit for children. The author suggests features and areas of content in continuing professional development (CPD) which she also argues could go some way to helping teachers improve their subject knowledge and subject application. The National Curriculum Evaluation Study reports that teachers of children with special educational needs (SEN) feel that science, especially practical science, has an important part to play in the development of all children. Laura worked in a special school and Keri in a primary school with a high proportion of children with SEN.