My 7th grade son was reading a book (part of a series) about a "battle" between boys and girls. There were tricks played on each other and they considered each other enemies... I'd like to get him the series but don't know where to begin..
He doesn't remember the author or title, he remembers characters names, Wally Hatford and Caroline Malloy. Can anyone help?

The book you are looking for is
Girls Take Over
By: Phyllis Reynolds Naylor

Thank you! With your help, there will now be a much appreciated Christmas gift for my son!!