Previous event-related potential (ERP) studies have revealed that faces and words show a robust difference in the lateralization of their N170. The present study investigated the development of this differential lateralization in school-age boys. We assessed the potential role of fetal testosterone (FT) level as a factor biasing the prenatal development of lateralization, and the role of reading skill and Verbal IQ as factors predicting left lateralization for words in childhood. The adult pattern of differential N170 lateralization for faces and words was not present in a group of 26 school-age boys. This suggests that N170 lateralization only appears with years of experience with these stimulus categories or with late childhood maturation. FT level measured by amniocentesis did not account for a significant part of the individual variability in lateralization. Verbal IQ correlated with the degree of left lateralization of the N170 to words, but this effect was not specific to language abilities and language lateralization. A strong correlation was observed between the degree of left lateralization for words and the degree of left lateralization for faces, and both lateralization scores correlated with Verbal and Performance IQ. Possible explanations for these results are discussed along with ERP correlates of words and faces in school-age boys. (Contains 2 figures and 1 table.)