They need real, tangible, meaningful threats. Corporal or social.
Doling out talkings-to, ISS, OSS, bad grades and repeat courses are a relative joke. I spent uncountable hours in ISS for truancy, was made to walk miles to school, kicked off the bus and walk miles home, served community service, and had many talkings-to. None of it was effective.
Expulsion is treated as far too extreme and should be far more regular as both an incentive to the student and to the parents. For many of these kids school is an impediment and a detractor and they would do far better for themselves in the work environment gaining experience over the course of the 3-4 years anyways. There are far more permissive environments in workplaces than there are in school that are better suited for the nature of certain inclinations and measures than that of school. There's also the possibility of restarting vocational education, which frankly, is a good compromise. But the current system is bullshit. And the bar is so low that diplomas are given out to nearly 90% of students which is flatly wrong as from what I've seen there are a lot more people who are either academically or behaviorally unsuited for employment or voting by any reasonable standard. Setting up clear failure modes are the guidelines by which many of these people would derive structure and meaning in their education, instead they're allowed a de minimis exception and passed into the world as acceptably educated and competent when the opposite is true. And that totally erodes the meaning of the accomplishment.