A strong positive correlation between student seating and exam scores

After the first exam in a class, your professor says she’s noticed a strong positive correlation between student seating and exam scores: “ The students who scored the highest sit in the front four rows every class,” she says. After class, a friend suggests you should both sit up front for the rest of the semester to improve your grades. Having read about correlation and causation, why should you be skeptical? What are some possible reasons that there could be a correlation between sitting up front and getting good grades? Could you design an experiment to test whether sitting up front actually causes good grades?