I was confused about why in anime, high school students were not allowed to work. I understand in real life that they have to have permission from the school. Maybe I'm just reading into it too much as a Westerner.
Schools and teachers of Japan in particular tend to be more involved in the lives of their students than in the West. The reasons may vary, as each school sets their own policies.
The main philosophy behind such policies is that students should be more focused on school (and extracurriculars). Their reasoning is that working it distracts from time they should be studying and fitting into society through a club activity. Not all schools have such policies, but there are some that have over zealous policies -- some reasonable, other not. Luckily, or unluckily it's up to the teachers to enforce these policies. Some teachers give leeway to strict policies, while other find it to be their job to enforce it to a T. The series reflects a bit of it for those that understand the context.
What is typically imposed on students is not something that they want or need by rather conformity within the established bounds and norms of modern Japanese society (which ironically can be very archaic).