To improve upon a posttest only approach when evaluating a new fraction teaching method, researchers can utilize a pretest-posttest nonequivalent groups design. In this setup, third graders in a treatment classroom take a baseline fraction test, receive the new instruction, and then take a final test. Concurrently, a control classroom takes the same tests but continues with traditional teaching. By comparing the pretest-to-posttest score changes across the two classrooms, researchers can better assess the intervention's impact. Nevertheless, preexisting differences such as varying teaching styles or distinct classroom environments remain potential confounding variables that could independently influence student motivation and math achievement.