Visible crew/equipment: When Joey is in Dawson's room, trying to tell him about her relationship with Pacey, she can't find the words and turns to leave. As she bends over to climb back out of his bedroom window, you can suddenly see a microphone wire protruding from the back of her white shirt. It's a visible vertical line, and as she continues to climb out the window, you can see that there is no mike pack on her lower back. (00:19:05)
Visible crew/equipment: When Joey is walking out to the pier to talk to Dawson, right after the wedding; the wind is blowing her dress back and you can see a prominent, solid line going up the front of her dress from about the waist up to the neck. I assume this is probably a microphone wire of some kind and not just a wrinkle, as the line is solid and protruding through the material.
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.