This article explores some of the common mathematical difficulties that 11- to 16-year-old students experience with respect to their learning of physics. The definition of "understanding" expressed in the article is in the sense of transferability of mathematical skills from topic to topic within physics as well as between the separate sciences and mathematics. It is argued that students who are taught the reasoning behind the processes are less likely to compartmentalise their learning. Some strategies, particularly concerning the language of mathematics, are discussed.