After Hours - S5-E21
Audio problem: Just after Audrey storms out of Pacey's apartment, after catching him with Alex; Pacey runs after her and they begin arguing in the street. Audrey makes a comment that 'it meant your arms around her, and HER tongue down YOUR throat' referring to The Kiss between Pacey and Alex. But then Pacey counters with 'well actually, it was HER tongue down MY throat' in sort of a comic way, as if he was correcting a backwards situation. But Audrey had just said the same thing! One of the Actors messed up their lines, probably Busy Phillips since Joshua Jackson seemed to have his lines correctly.
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.