Diary of Wimpy Kid book 3-The Last Straw by Jeff Kinney

Greg's dad, Frank, is on a mission - a mission to make this wimpy kid, well, less wimpy. All manner of 'manly' physical activities are planned, but Greg just about manages to find a way out of them. That is until military academy is mentioned and Greg realizes that he's going to have to come up with something very special to get out of this one...