Who is Jack from Every Soul a Star and what is their importance?

Jack is the third essayist. He lives with his mother, brother, and various stepdads. Insecure about his appearance and academic performance, Jack tends to keep to himself. When he fails his science class, Mr. Silver offers him the opportunity to go to Moon Shadow for the eclipse, in order to help him with an experiment and get out of summer school. While staying at the campground, Jack experiences a continuous stream of events that lead him to act in caring, thoughtful, intelligent and even heroic ways. This boosts his confidence and inspires him to rush back to the eclipse after running from it and put his hand into Ally's.