I was flipping channels last night, and came across the end of this movie, which I saw a gazillion times when I was a kid. My sister really loved it too. I spotted a production nit:

When Gary is racing in the red Ferrari to get Deb home, he passes his parents. In the long shot of the car doing a dangerous turn, it's pretty obvious that the stunt driver standing in for Anthony Michael Hall is wearing a really bad wig.