Ego Tripping at the Gates of Hell - S6-E7
Continuity mistake: When Jack is talking to Professor Freeman outside the book signing, there is a close-up shot of the Professor with a noticable strand of hair hanging off his right forehead. The next shot of him shows the hair smoothed, and the strand back into position. He didn't touch the hair, and his arms were down by his side the entire time. (00:24:15)
Ego Tripping at the Gates of Hell - S6-E7
Continuity mistake: When Joey is talking to Eddie at the doorway of her dorm room, a short brunette with her hair parted on her right side appears walking around the corner of the hallway behind Eddie. Joey and Eddie continue talking, and a short time later the same brunette again walks by in the hallway behind Eddie. She should have already walked past him in the time allotted before we see her again. (00:42:25)
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.