Critique of an Argument on Extracurricular Activities and GPA

The following is an argument presented in a newspaper editorial:

"A recent study has shown that students who participate in extracurricular activities tend to have higher GPAs than those who do not. Therefore, to improve overall academic performance, schools should require all students to engage in at least one extracurricular activity. This will not only enhance their grades but also foster better social skills and teamwork capabilities."

Critique the reasoning presented in this argument. Discuss any assumptions made, the validity of the conclusion, and how the argument could be strengthened.