What are the characteristics of traditional Muslim schools?

Traditional Muslim schools have no restrictions on the age of admission. Muslims, no matter how old they are, can enter schools and come in and out freely. There is no mandatory provision. Once students feel successful, they can go to a higher school for further study. Such traditional schools are open all day, so that adults who are working or have the burden of housework have the opportunity to learn knowledge. Traditional Muslim schools have no formal examination system and no graduation certificate after school. Students' grades and knowledge levels are evaluated by teachers. Such schools also have no study years, ranging from a few years to more than ten years, and some even decades.