While I do agree that you have to make it clear that this isn't on.
I think unless you also work on what is going on, you won't get anywhere.
At about this age my ds did a life assessment thing at school. They had to put in all sorts of things - what car do you want to drive, what sort of house do you want to have (eg detahced 4 bed in London
, do you want new iphone and a netflixs accout etc etc . Then based on that they were told how much money they needed to earn each month.
My ds did it fairly modestly, for example he knows London is expensive, so he chose Manchester, and not a BMW and so on.
he was pretty surprised at how much he needed to earn per month.
(the game added on for utilities and food etc)
Then they could look at certain jobs, how mcuh they paid, and if that matched their anticipated lifestyle.
It was a fun day, but I did notice a shift in attitude, real life lesson that if he wanted a decent lifestyle he needed to be able to earn it. He still did bare minimum for most of school, but enough.
13 is a classic age for thinking What is the Point of school. He may also need to talk about how some of the kids he likes to hang round with may not end up getting the exmas they need either. Learning to do what is right for you, rather than following the crowd.
I woudl do that in a working together type of way, rather than confrontational.