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Abstract Two years after the end of a two‐year intervention program intended to promote formal operational thinking, the achievement of students initially 12 years of age was tested by their results in British National examinations, taken at age 16. The intervention methodology was set within the context of science learning, so the difference between experimental and control classes was examined first in terms of their science results. The boys achieved an average of 40% more grades of C or above than the controls. This grade is the minimum criterion for higher education in Britain. The achievement was not found equally in all students: About 40% of the boys and 25% of the girls showed effect sizes of two standard deviations in relation to comparable controls, whereas the others did not differ from the controls. Both boys and girls showed significantly higher achievement in English than comparable controls, with an effect size about half that for science. The boys—but not the girls—also showed higher achievement in mathematics. It is argued that this evidence supports the interpretation that the students' increased science achievement was caused by increased general intellectual capacity, and not just by improved domain‐specific skills.
Shayer et al. (Tue,) studied this question.