SUMMARYDevelopmental data were obtained on the ability to discriminate between the sexes on the basis of dress, hair and genitalia. The focus of interest was on developmental changes in ability to discriminate on the basis of genitalia and in knowledge that the genital cue constitutes the critical characteristic. It was found that about half of a group of 7‐yr‐old children were able to discriminate on the basis of the genital cue while significantly more than half of the 9‐yr‐olds manifested such discrimination. However, it was only in the 11‐yr‐old group that more than half of theSs appeared to be aware that the genital cue is thedominantcharacteristic differentiating boys