In a study comparing two math textbooks, which factor could be a potential confound?

The experience of teachers is indeed a potential confound in a study comparing two math textbooks. This is because the effectiveness of a textbook might be influenced by how adept a teacher is at using that textbook, which relates to their experience. If one textbook is employed by more experienced teachers while the other is used by less experienced teachers, it becomes challenging to determine whether differences in student performance are due to the textbooks themselves or the varying levels of teacher effectiveness. Essentially, the experience level of teachers could skew the results by impacting the way the material is delivered and understood, making it essential to control for this variable in the study design to ensure that the results reflect the true effects of the textbooks rather than the influence of teacher experience.