In a 15-year study of thousands of children, including those with dyslexia and autism spectrum disorders, researchers discovered that a so-called core language skill, as identified here, was stable from infancy to adolescence. These findings affirm that when a child's language skills are lagging, early intervention is best. As an infant, grasping a language is one indicator of cognitive and social development. Children exhibit individual differences in competency, however; for example, individuals who are the same age can differ noticeably in terms of their language comprehension. It is important to know whether these differences shrink, grow, or remain stable over time, so that interventions can be timed optimally for children who struggle relative to their peers. Differences in language development can be seen in atypically developing children including preterm, dyslexic, autistic and hearing-impaired, compared to typically developing infants. But, little is known about how biological risk affects language stability in atypically developing children. Based on caregiver reports and direct assessments of children from the Avon Longitudinal Study of Parents and Children, Marc H. Bornstein and colleagues analyzed, in two groups, the stability of what they dubbed a core language skill over a 15-year period (starting when children were six months of age and lasting until they were 15). The first group consisted of 935 typically developing children. The second comprised a total of 5,167 children, 4,111 typical and 1,056 atypically developing children. Both groups exhibited clear evidence for individual variation in a core language skill at all ages. But, even when accounting for nonverbal intelligence, sociability, maternal age and education, an individual's core language skill abilities relative to their peers proved consistent from infancy to adolescence in all groups, except for babies between six months and one year old. The strong stability from very early in development suggests that lagging language skills should be addressed as early as possible (and long before school entry), say the authors.