tion programs for preschool children that follow the Montess

tion programs for preschool children that follow the Montessori method perform better than other pro- grams? A study compared five-year-old children in Milwaukee, Wisconsin, who had been enrolled in preschool programs from the age of three.17 (a) Explain why comparing children whose parents chose a Montessori school with children of other parents would not show whether Montessori schools perform better than other programs. (In fact, al the children in the study applied to the Montes- sori school. The school district assigned students to Montessori or other preschools by a random lottery.) ) In all, 54 children were assigned to the Montes- sori school and 112 to other schools at age three. When the children were five, parents of 30 of the Montessori children and 25 of the others could be located and agreed to and subsequently participated in testing. This information reveals a possible sou of bias in the comparison of outcomes. Explain why. (c) One of the many response variables was score on a test of ability to apply basic mathematics to solve problems. Here are summaries for the children who took this test:

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