It wouldn't be such a big deal to prevent adults from taking these jobs, it just needs to be more attractive for companies to give them to students. So, the low

It wouldn't be such a big deal to prevent adults from taking these jobs, it just needs to be more attractive for companies to give them to students. So, the lower wage alone would be a good enough incentive for them. Once the minimum wage was lower for "school jobs" the market would efficiently define which jobs can be given to school kids and which can't.