I think 5th or 6th grade reluctant readers would enjoy this mystery story -- the first in a series by Andrew Clements. The 6th grade characters (Ben & Jill) are likable enough, the maritime setting is appealing and the plot has not only mysterious clues but also a sinister school custodian (who seems to really be a company spy). There's an exciting sailing race at the end of the book (which felt a bit extraneous to the plot). I found the abrupt ending (which does not resolve too much) to be a bit frustrating -- obviously the hope is that kids will want to read the rest of the series. Those who liked Clements' other books should like this one as well.