First, I suppose I had better explain about our "school" for your better understanding, because our school is not such a formal school as you would often see in your country...
Here in Japan, children aged from 12 to 18 must study very hard in order to enter high-schools or universities. Yet, the public educational system in our country cannot provide them with enough educational services. Those formal public schools are only empty caves, where teachers gather to get paid their salary.(Trust me. I myself was a member of those garbage teachers several years ago. So I know everything about their internal situations. Most of the teachers in our country are certainly able officials, but they NEVER can be called educators.)
Still parents are not as stupid as our Ministry of Education. They fully know that their children cannot master enough knowledges & skills as long as they depend on public schools only. In order to reply to their demands, in this country, there are a large number of special private schools just like us.
Children comes to our school once or twice a week, after their formal school(Our classes start from 5:00p.m. and end to 10:00p.m. in the evening). We teach them math, English, and some other subjects there. Of course, it is not a volunteer work, but a business of ours. Could you see this? In our country, many(not all, though) parents have to spend their money both for public schools of daytime, and for private schools of nighttime. It is pretty hard for parents as well as for their children : (