This study examined the effect of low birthweight on school achievement and the mediating roles of cognitive and behavioural factors. The sample (115 females, 100 males) was selected from a longitudinal study of first-born singleton children, born between 1986 and 1988 of German-speaking parents, recruited from eight hospitals of the Rhine–Neckar region in Germany. Twenty-nine very-low-birthweight (VLBW; less than 1500g), 74 low-birthweight (LBW; 1500 to 2500g) and 112 normal-birthweight children (NBW; more than 2500g), all without severe neurological disability, were assessed at 11 years on cognitive, motor, scholastic, and behavioural measures. The scholastic measures included a school performance score and a teacher recommendation for type of secondary school the child should attend. LBW and VLBW children performed less well than the NBW group in all areas. LBW and VLBW groups remained at risk for school difficulties into late childhood, even when not neurologically impaired. Arithmetic, vocabulary, concentration, non-verbal intelligence, and attention problems were significant mediators of the effect of low birthweight on the school performance score. Arithmetic, vocabulary, motor skills, and attention problems were found to be mediating factors of birthweight on teacher's recommendations. The poor outcome of the low birthweight children could not be attributed to further obstetric risk factors. Parents and pediatricians should be made aware of specific long-term deficits of low birthweight children that may impair school performance, although they may be within a normal curriculum.