If you are thinking of taking MIT courses in the spring, you should be aware that due to the differences in the two institutions' schedules, MIT grades may not be recorded in time for Commencement. This means that though you could march at Commencement, you may not actually receive your diploma until October, so think carefully about whether, under these circumstances, you still want to take the MIT course.  At the very least, you will want to make your MIT professor aware that you are a Wellesley senior and have a conversation about when the final exam or project will be due and how grading will work.