Final answer:
Exercising 7 days a week leads to slightly higher grades for students, with a modest difference of 0.4 points. Exercise likely contributes to this through its various health benefits, but findings should be interpreted with caution regarding sample sizes and study designs.
Step-by-step explanation:
The impact of exercising 7 days a week on the grades of students is that the grades of students who exercised 7 days a week were slightly higher than those who did not exercise at all. This is indicated by the 0.4 point difference in favor of the students who exercised regularly. While this suggests a positive correlation between exercise and academic performance, it's important to note that this difference is modest. The benefit of physical activity on academic outcomes may also be related to the health benefits that it confers, such as improved cognitive function and psychological well-being. However, it's crucial to consider factors like sample size and the possibility of confounding variables when interpreting these findings. For instance, studies might show a significant positive correlation between exercise and academic performance but the confidence in the results would be higher if the sample size were larger and the study well-controlled.