Without grading students do not bother to study hard, cope with challenges, overcome difficulties

hey guys! i need all your help to be better in writing. thanks in advance.!
by the way, can you let me know that my essay is short?

Grade is a mark given in an exam for a piece of school work. Students need grades as an assessment for their capacity at school. Good grades are the target, which students have to achieve if they want to step up the higher classes. Therefore, I totally agree that grades encourage students to learn more.

Grades motivate competitive spirit among students. Indeed, students defeat with each other by studying hard to get high scores. For instance, when a student gets lower scores than his classmates, he might ask himself: " Why do not I have a high grade? How can he get this grade? is he better than me? I think we ourselves at least one time ask these questions.

Good grades provide students knowledge. Grades evaluate one's capacity and perform one's attitude towards studying. Obviously, if a student has low grades, it means he might not understand the lessons. Therefore, he needs to chance the way he studies so that he enable to understand lessons and master concrete knowledge next time.

In sum, grades are the essential part of one's studying. Without grading students do not bother to study hard, cope with challenges, overcome difficulties, or perform self-discipline. Therefore, grades motivate students to work harder.

Good grades are the target, which students have to achieve if they want to step up to higher classes.
It is short but could be shorter. Good Job!!! You are a good writer.

Grade is the kind of noun that needs "the" or "a"
A grade is a mark given in an exam or for a piece of school work.-- I used "or" because you can get a grade for an exam OR for a piece of school work.

Your thesis statement is good. However, do grades also discourage students sometimes?

Grades motivate and build competitive spirit among students.----- the grade does not motivate the spirit. It motivates the students. So, we should write:
Grades motivate students and increase competitive spirit.

Indeed, students defeat compete with each other by studying hard to get high scores.

Use a capital letter for the beginning of every sentence:
How can he get this grade? Is he better than me?

And I think this sentence needs "all"
I think we all ask ourselves these questions at least one time during our education.

This may be too short or it may not be. You have to find out by asking the teacher! Thanks for participating here! :-)