(From the pilot episode. Kevin and his friend Paul are in Kevin's bedroom reading his older sister Karen's sex education book Our Bodies, Ourselves. Actually, the book didn't come out until 1971, while this episode was set in 1968!)
NARRATOR (originally voiced by Arye Gross, later replaced by Daniel Stern): This was it. The last night of summer.
PAUL (Josh Saviano): Holy cow!
KEVIN (Fred Savage): Try not to drool on it, OK? If Karen finds out I have this, she'll kill me.
NARRATOR: Paul and I decided that the best way to prepare for junior high school girls was to look at them naked.
(Sound of a knock on the door. Shot of the door as Kevin's mother Norma opens it and looks in. Shot of Kevin and Paul looking at Norma off-screen with surprise, as Paul tries to hide the book by sitting on it. Close shot of Norma looking at them off-screen.)
NORMA (Alley Mills): Paul, your mother called. She wants you to come home right away.
PAUL: Well, I guess I'll see you at bus-stop.
PAUL: Last night I had a dream that...when I got to school I realized I had no clothes on.
KEVIN: If you're naked when you get to the bus-stop, I'll tell ya.
PAUL: Do you know what you're gonna wear?
KEVIN: Paul, I have no idea.
NARRATOR: Actually, I'd been planning my wardrobe for about six weeks.
(Transcript adapated from fansite http://mytwyyearbook.tripod.com/epsum.html)