I'm trying to remember the name of a book that I read in the 90's. It was a YA novel about a nerdy kid who was abducted by aliens and ends up travelling with them for awhile. There were a couple of sequels I believe, about how the aliens are going to destroy the earth unless the boy can prove there is some good here.
If it wasn't for being across sequels this sounds rather like Heinlien's Have Spacesuit—Will Travel.
Ha! That sounds like Bruce Coville's My Teacher is an Alien and its subsequent sequels.