Identify the threats to internal validity in each of the following experimental studies: a

Identify the threats to internal validity in each of the following experimental studies:

a. At the beginning of the school year, an elementary teacher set up reading stations in her room with supplementary reading materials in each. At the end of the year, she reported that the interest of her class in reading was higher than in any of her previous classes. She recommended that all teachers set up reading stations.

b. A researcher wanted to investigate the effectiveness of new teaching materials designed to increase students’ verbal skills. One class used the new materials, and another class used conventional workbooks. Both classes were given a test of verbal skills at the end of the semester.

c. A study was conducted in three thirdgrade classrooms investigating the effect of three methods of teaching math. The teacher could choose the method she wanted to use but could use only one method with her students. At the end of the semester, all the third-graders were given the same math achievement test.