Longitudinal research studies that follow at-risk samples before a disorder is evident, ideally from infancy, are the gold standard in the field of neurodevelopmental disorders (Goswami, 2014). They are also the rarest. In this issue of Brain, Clark and colleagues report a longitudinal structural neuroimaging study of children at high versus low risk of dyslexia that began before reading instruction commenced. The structural scans were taken the year before reading was taught (at age 6), a year after reading tuition began (at age 8), and after dyslexia had been diagnosed (at age 11). Clark etal.'s study thereby reveals the neurodevelopmental trajectory of the dyslexic brain, the only sure means of disentangling cause from effect in the aetiology of a neurodevelopmental disorder.
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