I think that the concensus here is that Math and Chess are not closely related as skills. I could never figure why it was so in my case. I love Chess, but my skill at the game is fairly ordinary, no matter how much effort I put in.
After the initial boost I got from learning about development, when my wins increased enormously, I still found that It was hard to get to a higher level.
The factor mentioned here a lot is memory. I can solve problems given time. But Chess players, I mean REAL Chess players forget nothing of either a concrete position, or the essentials of it. I never met a Chess player at a loss for words, or who talked sloppily.
This leads me to wonder if Chess has a grammar and a structure similar to language. Language adapts to the concrete reality, and finds a way to express an idea clearly and accurately, a Chess skill. Chess players never seem to have to work all that hard at the board. All they require is not to be distracted from thinking and concentrating, or losing their thread of thought.
It is futile to force Chess on anyone. You either love it, or it bores you to death, and is at best a useless exercise in pushing wood around.
There is also a strong competitive element in Chess. Much as we like to say so, we are trying to smash the other fellow. No one deliberately loses. When the game is over, the opponent is a companion in the love of the game, but until clock fall or mate or exhaustion leading to a draw, it is battle.
Playing the board is for puzzles. Some people for whom the Competetive instinct is not strong will love Chess for its challenge to the mind will enjoy composing positions, but they are rare (and might I say needed), and are a special type of person.
Chess in schools as an optional activity is fine and to be desired, but for most children, it is something they are not interested in, never will be, and is not essential for education.
Does it help develop the brain. I am sure it does.
The most useful aspect of Chess is that it does demand a certain tidiness of thought, and organizational skills. Most REAL Chess players have a capacity to see the big picture, to sort the trivial from the essential, and to see a plan through.
Have I contradicted myself? Maybe, but compulsory Chess is not necessary, although to learn the rules is not that hard. But after that, the children who like it should be encouraged, and those who do not should move on.
All those great benefits of chess will not happen to the kids who do not want to play chess. Articles like this one will just make ambitious (or despaired?) parents send their unwilling kids to chess classes. They will be noisy and obnoxious, ruining the fun and concentration of those who want to play chess.
Even worse is the idea to make chess compulsory, as chess constitutes a mental cruelty which should not be imposed on unwilling victims.
And whether chess is really so benefitial for learning is another question. Maybe it is, but then kids aready need to have the ability and willingness to concentrate and solve problems in order to improve those abilities.
In other words: Parents, leave your brats at home! I don't want them in my class! I only want kids who want to be there!