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.

Some people think that schools should select students according to their academic abilities. Others believe that young people with different abilities should be educated together. Discuss both these views and give your own opinion.

The opinions about the standard of enrolment vary from person to person. Some people believe it better to select students according to their academic abilities, while others argue that schools should educate schoolchildren with different abilities together. This essay will discuss both of the two views.

There are several arguments in favor of choosing students according to their academic performances. One of these is that schools can boost their efficiency of schooling. This is primarily because the educational administrators can arrange the curriculum effectively for students who have the similar academic abilities. An additional point is that when youngsters who perform well academically are gathered together, they can exchange their thoughts and ideas more easily and probably achieve consequential greater academic achievements. As a result, this may conduce to the cultivation of social elite, which is the third reason for this view.

On the other hand, to mix students with different abilities together is more advantageous to the development of individuals. Except the academic abilities, students’ survival in the society also demands more such as skills of communication, methods of organizing activities and leadership. All of these can be acquired by learning from other students with the corresponding abilities. Meanwhile, the atmosphere in schools can seem more active and dynamic when students show their distinct capacities, for example, for singing, dancing, and painting. Such educational circumstance really helps students balance their academic study with their leisure activities.

Personally, schools should accept students with various students and educate them together, since schoolchildren can benefit more from there. However, there is still a compromise that students could be divided into different classes based on their academic abilities.

STATISTICS

Number of characters (without spaces) : 1,567.00
Number of words : 275.00
Number of sentences : 15.00
Average number of characters per word : 5.74
Average number of syllables per word : 1.91
Average number of words per sentence: 18.40

It seems hard to me to write the essay with 10 to 15 words per sentence. Like my previous essays, the average number of words every sentence seems to stay at about 18.