I can't believe I finally found the title of this book! I remember reading this in elementary school, but for years I couldn't remember the title. I could have sworn it was something like "The Fourth Grade Caper" or something like that (turns out they were in third grade). I remember so much of the plot of the book, despite reading it 20 years ago.

Edit: I just re-read this, June 5 2008. It was still a lot of fun, and I really did remember sooo much of the plot and events. Back then though, it never occurred to me to ask whether the author is English. They're supposed to be English schoolkids on this trip, but I can't tell if the language reflected that or not. She used "car park" and "looked round" and "crikey" but there were other things the kids said that had me wondering.

Anyway... still enjoyable after 20 years!