Summary.This paper examines aspects of children's understanding of illustrations used as an adjunct to learning. It reports an experiment designed to determine whether first‐year secondary school pupils could identify the cut surfaces of objects in six biological illustrations taken from commonly used textbooks.The results show that few children were able to perform the tasks correctly but that the illustrations were not equally difficult. Picture analysis indicated that not only the features of the object depicted but also the number and type of pictorial conventions employed posed significant difficulties.It is concluded that the findings have implications both for theories of perceptual development and for the role of illustrations in teaching. It is suggested that teachers should regard the use of illustrations as learning aids as problematical and consider the need to teachaboutillustration