Qualitative and quantitative aspects on mathematics achievement in MZ and DZ twins

Mathematics achievement test results have been collected for 22 MZ and 24 DZ same-sex twin pairs in the Swedish compulsory school. The twins were approximately 11-13 years of age and attended grades 4, 5, or 6. The twin pairs were part of a larger collaborative study between Israel and Sweden (the KAM-project). Teachers were asked how they planned and evaluated their work in the subjects Swedish and Mathematics. In addition to this, results for the twins on Maths tests given by the teachers in their regular work were collected. These tests were thus used by the teachers as an instrument to evaluate the educational process. Intrapair similarity for MZ and DZ twins has been compared for qualitative and quantitative aspects of the Maths tests. Different tests were used by the teachers but the same criteria have been used in the comparison. MZ twins are somewhat more similar than DZ twins for both the qualitative and quantitative aspects. Only one quantitative aspects, however, percentage of correct answers, shows a significant difference between the twin categories. A comparison was also made of intrapair similarity in classes, where the teachers differed according to planning and evaluation of their education. Irrespective of that, the MZ twins seemed to be more similar than the DZ twins in number of correct answers on the Maths tests. Educational implications are discussed.