Blast from the Past — Meg Cabot

You can't have enough buddies...

Allie's excited about her class field trip, even if it's only to a historic one-room schoolhouse. But she gets to ride on a bus, which she usually misses out on, living so close to school.

But then Mrs. Hunter announces that every student in Room 209 has been assigned a "buddy" for the day -- from Allie's old fourth-grade class at Pine Heights Elementary -- and her buddy just happens to be her ex-best friend, Mary Kay, who betrayed Allie right before she moved! Allie is going to have to spend a whole day sharing an old desk with a big crybaby.

With her past catching up with her, it looks like this is one trip Allies going to need to write some major rules for.