I see no problem. especially since english is not your first language (Iassume since you live in Portugal) Good job, the only SLIGHT problem is syntax, which is understandable because the spanish and english syntax differ.
teach me english

yes and that seems to be the problem, in the first sentence:
There is a school in Portugal,
Or should it be
In Portugal there is a school

They refer to the interest demonstrated by the pupils on both chess itself and the other curriculum activity's.
demonstrated by the pupils in both chess itself.
the only error i could see. otherwise great english
Not helping that much :( lol

In english it can go either way. Your post was clear. If you post some other things they complained about, there might be more but from that passage you have a better grasp of english than some who speak it natively.

ok here is another :)
Chess really improves on yout concentration skills
Gives you the need to have a strategical view of the board to be able to play
An huge ammount of real life strategy such as the ones pointed out by Kasparov in "How chess imitates life" or even in that much less know book by that very badly know author Sun Tzu "The Art of War"
So we can say it prepares kids for the competitive world?
They are envolved in sport, so less time for drugs and other risk behavior by the pupils
If they are learning it as a group it helps them development relationships.
Its good for your memory altough not proved that chess players have a better memory then regular persons, its proven that the fact they are using the brain to remember moves keeps brain cells active and that prevents them from dying.
People who play chess are seen as "smarter" then the average by non playing people that as to be an advantage, it even help to insert chess in your resume!
Piece counting is an essential part of chess playing so you are always facing the need to do simple math, and it is well know that people don't improve on math by doing the hard exercices, but on repeating for an endless number of times simple math such as 2+3 or 8+7 etc, youl develop your brain in a way this tipe of thing is just automatic. So yes chess does improve your math skills.
Chess is fun and "pratical" in the sense kids do move the pieces and touch the board so they feel more connected to the game and the activity leaving them more interested.
There are more points about why chess is great to teach, ill let others say something about it now!

ok here is another :)
Chess really improves on yout concentration skills
Gives you the need to have a strategical view of the board to be able to play
An huge ammount of real life strategy such as the ones pointed out by Kasparov in "How chess imitates life" or even in that much less know book by that very badly know author Sun Tzu "The Art of War"
So we can say it prepares kids for the competitive world?
They are envolved in sport, so less time for drugs and other risk behavior by the pupils
If they are learning it as a group it helps them development relationships.
Its good for your memory altough not proved that chess players have a better memory then regular persons, its proven that the fact they are using the brain to remember moves keeps brain cells active and that prevents them from dying.
People who play chess are seen as "smarter" then the average by non playing people that as to be an advantage, it even help to insert chess in your resume!
Piece counting is an essential part of chess playing so you are always facing the need to do simple math, and it is well know that people don't improve on math by doing the hard exercices, but on repeating for an endless number of times simple math such as 2+3 or 8+7 etc, youl develop your brain in a way this tipe of thing is just automatic. So yes chess does improve your math skills.
Chess is fun and "pratical" in the sense kids do move the pieces and touch the board so they feel more connected to the game and the activity leaving them more interested.
There are more points about why chess is great to teach, ill let others say something about it now!
ok, let me take a stab at this one.
Chess improves your concentration skills. (your, not yout) It requires you to have a strategic point of view in order to succeed. (Must have subject before give. Gives and need do not mix very well, hence the all encompassing "requires." Also and i know this is more subjective than objective, but to play chess and to succeed at winning are two very different things in that one requires only the knowledge to correctly move the pieces while the other has a point of adding rational thought and objective evaluation to the picture)
A huge amount of stategy... needs a verb and by saying such as, you are entering a subordinate clause which runs to the end of the fragment sentence.
even in the much less known book "The Art of War" by the (don't understand your intentions in saying badly known, are you trying to mean not known or with a poor reputation?) Sun Tzu.
So can we say it prepares kids for the competitive world? (we can makes it a declarative sentence instead of an interrogative one)
They are involved in a sport, so there is less time for drugs and other risky behaviors. (kinda hard to explain this one other than to say that envolved is not a word, but it is clear what you meant so no biggie)* ("there is" is necessary because a subordinate clause requires a subject) (it's not risk behaviors because both risk and behaviors are nouns and nouns do not describe other nouns so you have to make risk an adjective "risky")
If they are learning it as a group (,) it helps them develop relationships. (nouns do not follow one another generally as is this case, change the noun to a verb and you're good to go)
It's (not its because you're (you are) saying it is not its possessive, i.e. its coat, its ball, etc.)
Thats all I can bring myself to comment on as I am not a big fan of English myself, but I do hope that this assessment is helpful to you.
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People have complained in several topics because of my bad english lol.
So this is my chance to learn just tell me what Im doing wrong or how I could explain it better, Ill try and correct it.
Here is a text I wrote about a chess school in Portugal
There is a school in Portugal, that just a few years ago started to teach chess as "mandatory" it is named "31 de Janeiro" located in Parede Portugal, they must be doing something right since they are now Fide world champs in U-10 and both the teachers and parents are quite happy about it and say everyschool should have it. They refer to the interest demonstrated by the pupils on both chess itself and the other curriculum activity's. If it works for them, it would work for others too, its just hard/expensive to start, but if you think about it what would be better. have your kids learning chess, or getting the school to rent a bus to be able to take your kids to the beach during the summer? Or tenis class, football, or some other sport schools offer to our kids. Obviously every sport as its advantages, but very few or even none offer so much benefits as chess does!