As long as you are taking classes (at least 1/2 time) the fall after you take the summer off your payments, or you grace period, wont start. If you are not taking classes, then your 6 mth grace period starts. Its very common for students to take the summer off.
As for taking fall or summer off, most lenders start the grace period, but as soon as you enroll in classes for the next semester (and your school completes the proper paperwork) -in this case summer - your status is again changed to student with no payments.