Identifying Flaws in Educators' Argument on Testing

In a recent discussion about the most effective ways to improve student performance in mathematics, a group of educators concluded that providing students with more frequent testing will prepare them better for their final examinations. They argue that this approach has worked in their experience, citing increased test scores and improved student retention in mathematics courses. However, critics of this strategy contend that merely increasing the number of tests can lead to heightened anxiety among students, ultimately harming their performance.

Which of the following most seriously weakens the educators' argument?