Assessment for learning is any assessment for which the first priority is the promotion of pupils' learning. The purpose of this current study was to explore the extent to which science teachers use assessment for learning when they teach biology in secondary classes. A year-long study with nine secondary science teachers in four schools in the greater London area was carried out. The teachers were observed during their teaching of theory and investigation lessons and they were interviewed twice. Findings show that only a few of them implemented elements of assessment for learning. It is argued that for science teachers to use assessment for learning in biology education, a clear understanding of the intended quality of performance on investigations is a prerequisite. Furthermore, it is explained how teachers may develop good questions and written feedback in marking.