They go thru a phase from about 11ish thru 14ish where it's like pulling teeth. (this is true of public school boys too, though!!) it's not anything you're doing wrong, just the way it seems to go. I found the carrot-stick approach worked best, where I controlled the access to the "good stuff" and then doled it out only after the work was done. People were often annoyed with me LOL but we did get through it eventually.

