Children, it is argued, fulfil sex-role stereotypes: boys are encouraged to play with toys which involve visuospatial manipulation; girls are not (we will come back to this in Chapter 12).

A child who enters the fifth grade a year earlier than a child of the same age in the fourth grade has a verbal IQ that is five points higher at the end of the school year. In Norway, there are indications that adding two years beyond the seventh grade affects (improves) IQ at age 19 (Brinch and Galloway, 2011).