Poor study on teacher quality

AAAS Science magazine reports this study:

Teacher Quality Moderates the Genetic Effects on Early Reading
J. Taylor, A.D. Roehrig, B. Soden Hensler, C.M. Connor, C. Schatschneider

Children’s reading achievement is influenced by genetics as well as by family and school environments. The importance of teacher quality as a specific school environmental influence on reading achievement is unknown. We studied first- and second-grade students in Florida from schools representing diverse environments. Comparison of monozygotic and dizygotic twins, differentiating genetic similarities of 100% and 50%, provided an estimate of genetic variance in reading achievement.

This is okay so far, except that "reading achievement" seems to be just reading aloud from a book, without testing comprehension.

Teacher quality was measured by how much reading gain the non-twin classmates achieved. The magnitude of genetic variance associated with twins’ oral reading fluency increased as the quality of their teacher increased. In circumstances where the teachers are all excellent, the variability in student reading achievement may appear to be largely due to genetics. However, poor teaching impedes the ability of children to reach their potential.

No, this does not measure teacher quality. One classroom might do better than another classroom for many reasons besides teacher quality, such as the IQ of the classmates and whether misbehaving students are disrupting the class.

The full paper is behind a paywall, but I checked it, and it admits that the study just assumed that test scores reflect teacher quality.

This is a simple twin study to quantify nature-nurture differences. Apparently, it had to slap on some bogus conclusions about teacher quality in order to get it published in a leftist science magazine.