At Home or at Preschool? Four sets of identical twins (pairs A, B, C, and D) were se...

At Home or at Preschool? Four sets of identical twins (pairs A, B, C, and D) were selected at random from a computer database of identical twins. One child was selected at random from each pair to form an “experimental group.” These four children were sent to preschool. The other four children were kept at home as a control group. At the end of the year, the following IQ scores were obtained:

Does this evidence justify the conclusion that lack of preschool experience has a depressing effect on IQ scores? Use the p-value approach.