
Coming Home - S4-E1
Revealing mistake: In the first scene, Pacey says something like see I think we should probably drop anchor here, have a bite to eat (and other things)... As he's walking around the boat, the camera shifts over and you can see two ropes that indicate the boat is already anchored or docked to something.
Answer: They are not twins (Jack is older than Andie). It is possible due to when birthdays fall in the school calender for non-twin siblings to end up in the same grade. Say that you have to be 5 on Sept 1 to start Kindergarten, you are born on Sept 2, 2000 and your little sister on Aug 30, 2001. Sept 1, 2005, you are 4 years and 364 days and can't start. So Sept 1, 2006, you are 5 years and 364 days and your sister is 5 years and 1 day, and, voila!, you're both in the same grade.