Continuity mistake: During this scene towards the end, Bessie insists on putting lipstick on Joey for Graduation. She dabs it on quickly, and there appears to be a noticeable smudge or mark on Joey's upper right lip from the lipstick. But the next shot of Joey, the lipstick suddenly appears normal and perfectly applied, and the smudge is gone. (00:33:40)
Continuity mistake: When Dawson is helping Gretchen to hang mistletoe, his arms change position instantly between shots, from laid on the ladder, to above his head touching the mistletoe.
Continuity mistake: In the scene where Jack is fired Jen is limping. She doesn't have the limp in any other scene and never hurts herself, it comes from nowhere and then disappears.
A Family Way - S4-E5
Continuity mistake: When Dawson is coming down the stairs to talk to his parents in the living room, there is a shot of Gail and Mitch on the couch together. Gail is sitting in such a way that her legs are draped over Mitch's legs, and her right leg is specifically hanging over his right leg touching it. But in the next shot, they show Gail and Mitch from the other side of the couch; and suddenly she is sitting with her legs up, bent at the knees and Mitch has his right leg up. There wasn't enough time between shots for anyone to move.
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.