Hi Chenyu Lue and thanks for this essay.

The body of your essay is fine

The weakest parts are the introduction (very weak) and the conclusion (a little vague at the end). Work on introductions for the next few days. Have a look at the site and look for different intros.

Intro

There are some big problems with your introduction. The first sentence is off-topic. The second one is just too similar to the question. It will not be included in your word count! The third sentence could be used in a million essays. Try to make everything specific to the topic.

Here’s one possible rewrite. I’m going to use description-of-the-situation intro (you can read more about Introductions here).

Situation: In some schools more academically able students and less able students are put into separate classes. Two sides: Although this is done for a variety of reasons, not all parents or students agree with it. Thesis: In this essay, I will explain why I think students should be educated together in most cases.

Word Choice/Word Form/Usage

• This essay will discuss both of the two views. → This essay will discuss both these views.
• All of these can be acquired by learning from other students with the corresponding abilities.  →  All of these can be acquired by learning with students with different abilities.

You wrote:

Except the academic abilities, students’ survival in the society also demands more such as skills of communication, methods of organizing activities and leadership.  →

We need to (1) make the list parallel, (2) fix article problems, and (3) change the word choice of ‘Except.’  Here’s one possible rewrite:  

In addition to/ Apart from academic abilities, survival in society also demands skills such as communication, organization and leadership.

Ideas

You wrote:

• As a result, this may conduce to the cultivation of social elite, which is the third reason for this view.

The phrase "cultivation of social elite" needs explanation and support. It’s not fully developed. Not everyone will understand you. Have a look at the official descriptors for IELTS Task 2 Writing (public version) here, under Task Response, and look for “some [ideas] may be inadequately developed/unclear”

This one also needs support or clarification

Meanwhile, the atmosphere in schools can seem more active and dynamic when students show their distinct capacities, for example, for singing, dancing, and painting.

Are brighter students not able to sing or paint?

Coherence and Cohesion

• Such educational circumstance really helps students balance their academic study with their leisure activities.

What does ‘such educational circumstance’ refer to? Instead of using ‘situation/condition/circumstance/phenomenon' or other vague words, specify! Here's a possible rewrite:

Having students in classes with a wide range of abilities and not just academic skills can provide balance and stimulation and be a better model of society.

Conclusion

You wrote:  

However, there is still a compromise that students could be divided into different classes based on their academic abilities.

Where? Why? What is 'the compromise'? Where did you mention it? If you mentioned it, repeat it in your conclusion. This is too vague! The conclusion should summarize and be quite specific.

Overall the essay is clear. You need to work on introductions. A small amount of work here will be very worthwhile.