--- - |2+ Background Among adults with schizophrenia, evidence suggests that premorbid deficits in different cognitive domains follow distinct developmental courses during childhood and adolescence. The aim of this study was to delineate trajectories of adolescent cognitive functions prospectively among different groups of youth at‐risk for schizophrenia, relative to their typically developing (TD) peers. Method Using linear mixed models adjusted for sex, ethnicity, parental occupation and practice effects, cognitive development between ages 9 and 16 years was compared for youth characterised by a triad of well‐replicated developmental antecedents of schizophrenia (ASz; N = 32) and youth with a least one affected relative with schizophrenia or schizoaffective disorder (FHx; N = 29), relative to TD youth (N = 45). Participants completed measures of IQ, scholastic achievement, memory and executive function at three time‐points, separated by approximately 24‐month intervals. Results Compared to TD youth, both ASz and FHx youth displayed stable developmental deficits in verbal working memory and inhibition/switching executive functions. ASz youth additionally presented with stable deficits in measures of vocabulary (IQ), word reading, numerical operations, and category fluency executive function, and a slower rate of growth (developmental lag) on spelling from 9 to 16 years than TD peers. Conversely, faster rates of growth relative to TD peers (developmental delay) were observed on visual and verbal memory, and on category fluency executive function (ASz youth only) and on matrix reasoning (IQ) and word reading (FHx youth only). Conclusions These differential patterns of deviation from normative adolescent cognitive development among at‐risk youth imply potential for cognitive rehabilitation targeting of specific cognitive deficits at different developmental phases. - Journal of Child Psychology and Psychiatry, Volume 59, Issue 11, Page 1215-1224, November 2018.