Data from national sample of 3- to 16-year-olds show that lower test scores and increased behavior problems of children of younger mothers resulted from family background rather than maternal age. For nonfirstborns, maternal age at first birth, not at child's birth, influenced test scores. Disadvantage of children born to younger mothers was reduced when family background was controlled. Maternal age was not important in predicting children's test score improvement. (Author/KB)