Plot hole: When Pacey and Andie are talking at the Senior Party, she excitedly mentions that he will be in the Caribbean that Summer. Pacey says that Andie would be in Florence, Italy. This doesn't make sense, because at that point in the episode, none of Andie's friends knew she was returning to stay in Italy. In fact, later during the graduation ceremony, Andie is talking to her brother Jack. He is the first person she tells the news to, and even says, "I haven't told anyone else this". So how would Pacey know the night before that Andie had decided to stay in Italy longer? (00:30:45 - 00:37:25)
Plot hole: After Drue has spent the night at Jen's house, Grams explains to Jen that she had a nice talk with Drue right after Jen left for school. But this doesn't make sense, because why would Jen have to be at school a certain time, and Drue not go to school at the same time or at all? His attendance at school would have been required as well.
Answer: It's only explained once in the series. Jack says to Andie "I tried to start kindergarten without you", meaning Andie was smart enough to start school early.