Writing prompt: Is It Necessary to Attend Training Classes?

Student essay:
Nowadays the students are mainly judged by there scores. In order to get better notes, more and more of them are having extra classes, sacrificing their own time on the weekend.
In my opinion, it's unnecessary for them to attend training classes.
When the students attend the extra classes, they won't concentrate themselves on the classes in their school. They'll consider it not serious to take a rest in the normal classes, because they can make it up on the weekends. They won't even do their homework seriously.
When the students attend training classes, they also don't have adequate time to have a rest or do some activities they really enjoy. Sometimes they even don't get enough sleep, and it'll directly lead to their inefficiency in the school.
Only when we make the best use of the classes in the school can we learn better. We can find our short points through doing our homeworks, and if we have any questions, our teachers are always glad to answer them. Attending training classes is just a waste of time and money.

Corrected essay:
Nowadays the students are mainly judged by their scores. In order to get better scores, more and more of them are having extra classes and sacrificing their own time on the weekend.
In my opinion, it's unnecessary for them to attend training classes.
When the students attend the extra classes, they won't concentrate on the classes in their school. They'll consider it not serious to take a rest in the normal classes, because they can make them up on the weekends. They won't even do their homework seriously.
When the students attend training classes, they also don't have adequate time to have a rest or do some activities they really enjoy. Sometimes they even don't get enough sleep, and it will directly lead to their inefficiency in school.
Only when we make the best use of the classes in school can we learn better. We can find our shortcomings through doing our homework, and if we have any questions, our teachers are always glad to answer them. Attending training classes is just a waste of time and money.