I remember this book very warmly, but I don't remember enough details to rate it, so I'm giving it 3 stars for memorability. Why, you wonder, am I adding it now? Because I just found out that Gail Hamilton is a pseudonym of Barbara Cocoran! Here's the story:

http://collectingchildrensbooks.blogspot.com/2009/08/class-reunion.html

I need to track this down and re-read it. It's looking a little grim, though. Neither my library nor Paperback Swap list it.