Hi Pedram_vaziry and thanks for this essay.  (And thanks Brian for your comments!)

Try not to panic about the exam on Saturday. Just get plenty of sleep the night before and  bring plenty of sharp pencils to the exam! Make notes, underline, and highlight in the reading and listening, and make a plan or brainstorm in the writing.

 Here are some comments on this essay:

Word Choice/Word Form/Usage

• A great competition between schools to attract more students causes to make the teaching hours longer and longer.  →
  Increasing competition for students between schools is leading to longer teaching hours.     OR        
  Increased competition for students between schools is leading to longer teaching hours.
     
• In order to reach this→ In order to achieve this
     
• Nowadays, going to a famous university is one of the major problems which students have to overcome. →
  Nowadays, trying to get a place in a famous university is a major concern of students.    OR           
  Nowadays, students are very anxious to get a place in a prestigious university.      
   
• this kind of problems → this kind of problem
   
• they can live better and more comfort → they can live better and more comfortably
     
• Therefore, it is essential to study harder in regard to being successful in university entrance exam → Therefore, it is essential to study harder to be successful in the university entrance exam
     
• Hence schools should make a hectic schedule for learning hours → Hence schools should offer/provide/have a busy schedule   (hectic is usually a negative word)

Shorten/Simplify

You wrote a29-word monster in your conclusion:

Hence schools should make a hectic schedule for learning hours and beside that it is important  to have an ample exercise hours in order to have a healthy society. (29 words)

Here’s one possible rewrite:

Schools should offer a busy and varied schedule with a balanced mix of sports and academic subjects. The result will be happier students and a healthier society. (27 words, 2 sentences, average 13.5 words per sentence).

Punctuation: Commas

You wrote:

Thus, the hardship of decreasing in exercise hours which students have to bear, give them an opportunity to live better in future. (22 words)

Don’t use commas to separate the verb (‘gives’) from its subject (‘the hardship’).  I recommend cutting back on commas: If in doubt, leave them out.  Here’s one possible rewrite:

The hardship of fewer exercise hours can lead to better exam results. (12 words)

Generic sentence/ Ideas

This sentence from Paragraph 3 could be used in a million essays, and it’s also not quite correct:

On the contrary, this matter has some drawbacks which we cannot ignore

‘On the contrary’ is not used correctly here.  Try to make every sentence in your essay related to the topic. This is a topic sentence, so it should give the reader a hint of what it coming or a preview of the paragraph. Here’s one possible rewrite:

However, less sport in school can affect student health.

You only have one idea in Paragraph Three -  health.  Don’t start to write until you have three ideas for each body paragraph. Wrapping many words around an idea still leaves it as just a single idea -  you need more ideas.  Here are some you could have used:

• Sports build character. Students have to learn to win and lose.
• Sports are fun.   A school without fun would be so boring that many students might drop out.
• Sports provide variety. Our brain switches off if only the academic part of it is used.
• Sports teach tactics. Politicians, businessmen, and administrators can learn valuable lessons on the field
• Sports encourage healthy eating habits. These habits can last a lifetime, even if the person stops playing sports.
• Sports teach teamwork. To succeed in most jobs nowadays, you have to be able to work as part of a team.
• Sports build bonds. Friends made on the field or on the track can last a lifetime.
• Sports teach balance. Students can begin to learn that their future lives must balance academic, social, family, work, leisure and community demands.
• Sports are great for a school’s reputation. The top schools often have the best teams, as well as the best academic results.
• Sports let different students shine. Not every student is going to be top in physics or chemistry.
• Sports attract students. Many students enroll at schools with good sports programs.

These are only a few reasons for having sports in a secondary school.  Really, if you have some ideas, the essay falls into place and needs no padding. Spend 5-9 minutes planning before you start to write, and don’t start until you have so many ideas that you are able to choose the best ones.

It’s like a car journey. You have to have enough petrol to get you to the destination. There are no gas stations on the IELTS Task 2 highway where you can stop to pick up new ideas and inspiration. Get them before you start.

Ideas

You wrote:

Decreasing exercise hours leads to some problems and diseases such as heart attack and obesity.

This is true, but while obesity is an issue in schools, heart attacks are usually only found among the staff. Make sure ideas are developed and supported fully. Do you mean health in school or in later life? Both are good -  the reader just needs to be certain what you mean.

You wrote:

some schools tend to have academic session in lieu of exercise classes. → some schools are replacing sports and physical education with more academic classes

The sentence was too weak. Try to avoid ‘tend’ unless you really need it.  In the introduction you need to make your points very clearly.

Overall...

Overall, Pedram, the most important point here is ideas. There are not many grammatical errors, and only a few word choice errors, so well done on eliminating those. Now just make sure to brainstorm and get more ideas. The more ideas you have, the easier your essay will be to write -  and read!