Nineteen children who had EEG diffuse slow frequency profiles suggesting a maturational lag were retested 1 to 2 years later receiving both EEG and psychometric assessments. They were compared to 18 children who also had been tested previously but did not have the slow frequency profile. Children with the maturational lag profile displayed varying degrees of EEG developmental change upon retest; i.e., some showed the expected developmental change while others remained the same. Within this group, there were significant relationships between the degree of EEG change and psychometric scores. Those that demonstrated the most EEG change had higher psychometric indices, and these relationships were not obtained in the comparison group. These findings suggest developmental heterogeneity with respect to brain maturation as measured by the EEG and also suggest that test-retest EEG data can clarify a maturational lag diagnosis.