There is general concern about the levels of noise that children are exposed to in classroom situations. The article reports the results of a study that explores the effects of typical classroom noise on the performance of primary school children on a series of literacy and speed tasks. One hundred and fifty-eight children in six Year 3 classes participated in the study. Classes were randomly assigned to one of three noise conditions. Two noise conditions were chosen to reflect levels of exposure experienced in urban classrooms: noise by children alone, that is classroom-"babble", and "babble" plus environmental noise, "babble and environmental". Performance in these conditions were compared with performance under typical quiet classroom conditions or "base". All analyses controlled for ability. A differential negative effect of noise source on type of task was observed. Children in the "babble and environmental" noise condition performed significantly worse than those in the "base" and "babble" conditions on speed of processing tasks. In contrast, performance on the verbal tasks was significantly worse only in the "babble" condition. Children with special educational needs were differentially negatively affected in the "babble" condition. The processes underlying these effects are considered and the implications of the results for children's attainments and classroom noise levels are explored. (Contains 3 tables and 1 figure.)