This paper provides a selective review of data on phonology, audition, vision, and learning abilities in developmental dyslexia, with a specific focus on patterns of normal alongside poor performance. Indeed we highlight the difficulties of interpreting poor performance, and we criticize theories of dyslexia that are exclusively suited to explaining poor performance, at the risk of overgeneralizing and predicting deficits in many more situations than are observed. We highlight a number of tasks and conditions where individuals with dyslexia seem to show perfectly normal performance, and we discuss the value of taking such data seriously into account and the difficulties of current theories to explain them. Finally, we discuss the experimental challenges for tasks investigating the nature of cognitive deficits in dyslexia and in other developmental disorders and the challenges for any proper theory of dyslexia aiming to explain cases of normal as well as poor performance.