Let them fail at their own cost. Let them realize that their own laziness is their own downfall.

What if they finish it within the first 15 minutes or so? They're forced to stay the entire time, and eventually get bored, leading to obnoxious noises and sounds, distracting those who need all the time. It would also help if they treated it like tutoring, not prison.

I understand going to ASI if you need help, or as a punishment, but not completing an assignment isn't a good reason for going. Most people go to "intervention" for not doing homework, not because they didn't understand, but because they just don't care. Making them stay after school doesn't have an effect on them. Let them fail at their own cost.