Our research is concerned with the underlying causes of reading difficulty. There is good evidence that some cases of reading difficulty (termed dyslexia) are caused by biologically based cognitive deficits. However, research into the causes of dyslexia is impeded by two main complications. Firstly, there are many possible cognitive deficits that could result in the same profile of reading difficulties. For example, a deficit in processing visual information, auditory information or speech sounds could each result in difficulties in translating written text into speech sounds, and therefore reading problems. Secondly, it is also possible to develop reading difficulties in the absence of a basic cognitive deficit, for example through inadequate instruction. We will use a comprehensive approach to measure the relative influences of different cognitive deficits, and a successful reading intervention to distinguish between experiential and cognitive causes of reading difficulties. Specifically, we aim to uncover the cognitive deficits that are associated with a reading difficulty that exists even under improved teaching. This research will help to uncover the cognitive deficits that cause dyslexia and will indicate which cognitive tests can most accurately identify pre-readers at risk of developing dyslexia.