Understanding in science relies heavily on an ability to handle mathematical concepts confidently. It has been shown that numeracy is an important area which pupils need to develop (Gill 1995; Lenton and Stevens 1999). This chapter looks at some of the key areas in science which are at risk if pupils are not numerate. It may be that some of these difficulties arise through not distinguishing between the teaching of facts and skills and the teaching through conceptual understanding. Suggestions both for student teachers and existing teachers of science in primary and secondary schools on how this problem might be addressed are discussed.