From what I can see, the author did an excellent job resolving the myriad different threads in the story, especially those involving the central characters. Noah, who is forced to spend the summer at Century Village, realizes that he has learned a lot from the experience and has come to appreciate the people there. Nadia has come to terms with her parents' divorce, and Ethan has learned to come out of his shell, having found the courage to do so at Sillington House. Julian has carved a niche for himself with his new classmates on the academic team, and Mrs. Olinski has evolved into a confident and effective teacher. Hamilton Knapp is exposed as the mean, conniving student that he is, and receives his comeuppance, having lost the adulation of his peers.
The threads about Epiphany's sixth grade academic team, the Souls, are neatly tied up by the author as well. Mrs. Olinski chooses her team and chooses wisely; the team is exceptionally cohesive and goes on to achieve the unprecedented feat of winning the Academic Bowl, after having competed with a series of teams which are much older than they are. And, in the final line of the book, the only remaining question regarding the team is resolved. Mrs. Olinski has, throughout the narrative, wondered how exactly she did choose her team. At the end of the story, she at long last comes to the realization that, while she did choose her team, they chose her as well.
The only thread I can think of that might have been left unresolved in the book is a minor one, concerning a minor character, Dr. Rohmer, the District Superintendent for Clarion County. Dr. Rohmer is a pompous, self-serving man, and his stubborn insistence on controlling what is said at the press interview concerning the Souls backfires on him, making him look very foolish in the public eye. When we last see Dr. Rohmer, he has grown "as pale as the paper of his unsigned contract". It is clear that his job may be in jeopardy, but I don't think we ever know for sure if his contract is extended or not (Chapter 9).