The Last Straw: Diary of a Wimpy Kid, Book 3 (Unabridged‪)‬

Greg Heffley will never change his wimpy ways...somebody just better tell Greg's dad that. Frank Heffley actually thinks he can get his son to toughen up, and he enlists Greg in organised sports and other 'manly' endeavours. 

Thus far, Greg manages to sidestep his father's efforts, then comes the threat of military school, and Greg realises he has to shape up or ship out!