Cram schools in Japan

Nowadays, almost all junior high school students go to cram schools (juku in Japanese) after school hours in Japan.
A custom of going to cram schools has been famous (or infamous) worldwide as important part of Japanese education, but it was basically only for students who wanted to enter good high schools (leading to prestigious universities) when I was a child.
In contrast, it seems rather strange now for a student not to go to juku, regardless of which high school he or she wants to attend. 
Moreover, juku is not just for third-year students who are urged to study harder as they have to take the entrance exams, but it is also an ordinary choice to take classes at juku even for first-year students.

So cram schools tend to be crowded, thus it is quite difficult for juku teachers to increase the academic level of each student.
To make things worse, students cannot concentrate themselves on study there because their friends, too, attend the same classes.
In this sense, many cram schools are just an extension of official schools.
Many students say, "my classmates attend cram schools, so I am going too."
Their parents lament, "it is like pouring money down the drain as it doesn't seem to make any favorable effect on the test scores of my child, but other parents have their children go to cram schools, so we cannot but do the same (this is a typical Japanese way of thinking)."

My student also went to a cram school before, but because he was shy, he couldn't ask teachers about what he didn't understand, and as a result, he fell behind other students in the juku classroom.
Finally, he quit the cram school.
I guess there are many others like him, but there is no practical solution in cram schools for this kind of problem because, as mentioned above, the classrooms are too busy for the teachers to care for each student.
Alternatively, it is only home teaching that such students can choose to improve their school performance.

By the way, why do junior high school students have to attend cram schools in the first place?
The classes at school are not enough for them?
I've heard many times a conversation among parents that "when we were students, it was enough for us to sit and listen to what teachers say in the classroom, then we were already sure we could pass the entrance exams."
Yes, that may be still applicable, but unfortunately, both the skills of school teachers and the academic standards of students are considerably lower than those in our school days, so most of students and their parents are worried about the exams and they are inclined to think that "we need to do something more."
It is difficult to explain the problems of school teaching here clearly, but I am aware of them in teaching him.

I will write about them here in the future.
Anyway, I have a responsibility for his success next spring.
Oh, no!