Thanks Youtthasack (joe) for the essay.

Essay Length

You are very honest to tell us that it took you 100 minutes. With practice, you will get faster, but remember you only have a recommended 40 minutes in the exam for Task 2 (Task 1 has a suggested 20 minutes).

And make sure you reach 250 words - there is a big penalty if you go below that number. There is no penalty for going over 250, but many students who write more than 300 or 350 words suffer as a result of spelling, grammar and poor organization.

It's a game! Keep practicing with a timer or a clock (there are some at the top of this page) and you will get there. Do 10 minutes today on a topic, and add one minute every day. Watch your word count increase!

Introduction

I would leave out the "highly-debated" bit completely, even though Alison tried to fix it. It's used by too many students. Why not ask a question or two?

Should my children learn about sex education from a teacher? Or is it my responsibility to teach it at home?

You could also do a past/present introduction

In the past, most children learned about sex from each other or from what they saw on the farm or in films. Today, however, many schools are beginning to teach sex education in class. Is this a good development? In this essay, I will ...

You can find other examples of introductions here.

I like your last sentence (thesis sentence) in your intro

This essay will show two reasons why should children at the age of 12 to 19 should be taught sex education in schools.

It's a good thesis sentence. It tells the reader that there will probably be two paragraphs (one for each reason) explaining why teenagers should learn about sex education. It gives your opinion, and tells the reader what is coming. Well done.

Sentence Structure

Some of your sentences are like spoken sentences. To make them like writing, especially academic writing, you need to make them shorter and tighter

The children in the age of 12 to 19 are physically in the period of sex changing so why not they have a right to learn about this physical turn.

Children between 12 and 19 have a right to learn about the many physical changes in their bodies.

Develop your ideas fully

You add an example (e.g. sex organ) to the first idea, but you could have added an example for the second idea in Paragraph 2. You wrote:

In addition, they will realize some strange feelings that emerge such as passion toward the opposite gender.

It's ok, but not enough. You could add

Teenagers need to realize that hormones in their body are changing not just the way they appear, but also how they think and behave. This can help them to recognize the difference between their feelings and reality, and even avoid depression or recklessness.

In paragraph two you wrote

Such problems like as early marriage, pregnancy and rape crimes are triggered from by sex abuse.

It's a big generalization. You need to avoid generalizations in IELTS (see the descriptors under Task Response). Sexual abuse is usually understood as an older person with a younger or underage person. This idea is not fully explained or developed (see Task Response again), so it's not very clear.

You could write

Problems like early marriage, pregnancy and rape have become more common. Sex education might help to reduce these problems. For example, if teenagers discussed the difficulty of being parents and raising children while still in school, it might make them be more careful. Similarly, if girls or boys do not know how their bodies work, what might seem safe might lead to unwanted or unplanned pregnancies.

If you develop your ideas, you will have no problem reaching 250 words. Your job is to make it easy for the reader. Don't think that the reader knows everything. You have to tell them.

Conclusion

Your first sentence is a bit too repetitive. How could you change it so that it sounds different?

In conclusion, I strongly say that there are at least two reasons for sex education to be taught to children in the age of 12 to 19 in schools.

In the last sentence:

According to the children right and to get rid of sex abuse, the school curriculum should adopt it.

I would change the word 'according' and simplify the structure

Schools should adopt sex education to inform children about their bodies and to reduce the number of sex-related problems in society.

Good luck with your timing and word count! 

Hi Alison, Joe

You could add questions in your introduction like this

Should children learn about sex in school? Or is it their parents' responsibility to teach their children when they think they are ready? In this essay, I will say I why I think sex education should be on the curriculum in school  

You could start with a situation, and then question it:

Many children learn about sex from jokes or comments from their peers. But is this the best way for children to learn about something so important? I will explain why I think formal sex education is necessary in order to prevent misinformation and embarrassment. 

Here's the opposite opinion. Again it's a situation, and then a question about the situation.

In some countries, children have lessons in sex education in their schools. But would you really want something so important left to teachers, or would you like your child to have to discuss such a private matter in class? This essay will explain why I completely oppose sex education as part of the school curriculum. 

You can also (re)use questions in your conclusion.  Don't go overboard with questions (don't have too many). One or two is enough in an essay. After all, the IELTS examiner already asked you a question, so it's your job to give an opinion, not just to ask another question back! 

Alison, I think that's good summary -  more examples would make Joe's essay easier. Joe, what do you think?