Dingus / Andrew Larsen.

Enhanced descriptions from Syndetics:

Summer vacation is starting, and soon-to-be-sixth-grader Henry is facing two months with nothing to do. He can sadly feel himself "being pulled by the gravitational force of nothingness." His best friend, Max, who may not even be his best friend anymore, is going away to chess camp. And all Henry's stay-at-home father has planned for him and his toddler brother, Sam, is something called a staycation. Things start looking up, however, when he finds out they'll be dog-sitting his grandfather's dog, Rupert. That is, until the day they bring Rupert to the park, where Henry does something irresponsible. Something with real consequences. And suddenly Henry would give anything to go back to the nothingness. Can Henry make things right? Or has he turned into the dingus Max said he shouldn't be? This classic middle-grade coming-of-age novel from popular author Andrew Larsen is told with humor and heart. Henry is a likable boy trying hard not to be a dingus (translation: "a fool or a goof") as he navigates the changes in both his home and social lives. On top of that, he knows his father is right when he says Henry needs to step up and become more responsible. Happily, Henry manages to do just that in the end. With believable dialogue and touching scenes of everyday family life, this story feels honest and true. It would make a perfect summer reading choice. It could also easily spark discussions about growing up and developing a sense of self.