As someone who worked in the area of Intelligence training I am very, very skeptical. For example, there was a burst of optimism about training working memory through Dual N-Back tasks, bought about by a revolutionary paper from Jaeggi et al. Then... not quite nothing but close.
I suspect there's a reason that no braining activity, ever, has been consistently shown to improve intelligence at the construct level. It may be that more specific capacities related to intelligence (like working memory) are improved, and that these affect life outcomes and practical capacity to grasp concepts etc, but this has yet to demonstrated to my satisfaction.
But I think the performance on IQ tests for people at the top have been going up, at least until recently. It could be, however, that you are right and the increase in IQ test performance reflects real gains in intelligence for those in the bottom, but fake "just getting better at taking tests because of repeated exposure to tests" gains for everyone else.
I continually train my ten-year-old son’s working memory, and urge parents of other young children to do likewise. While I have succeeded in at least temporarily improving his working memory, I accept that this change might not be permanent and could end a few months after he stops training. But I also believe that while his working memory is boosted so too is his learning capacity.
I have a horrible working memory that greatly hindered my academic achievement. I was so bad at spelling that they stopped counting it against me in school. In technical classes I had trouble remembering what variables stood for. My son, in contrast, has a fantastic memory. He twice won his school’s spelling bee, and just recently I wrote twenty symbols (letters, numbers, and shapes) in rows of five. After a few minutes he memorized the symbols and then (without looking) repeated them forward, backwards, forwards, and then by columns.
My son and I have been learning different programming languages through Codecademy. While I struggle to remember the required syntax of different languages, he quickly gets this and can focus on higher level understanding. When we do math learning together his strong working memory also lets him concentrate on higher order issues then remembering the details of the problem and the relevant formulas.
You can easily train a child’s working memory. It requires just a few minutes of time a day, can be very low tech or done on a computer, can be optimized for your child to get him in flow, and easily lends itself to a reward system. Here is some of the training we have done:
The key is to keep changing how you train your kid so you have more hope of improving general working memory rather than the very specific task you are doing. So, for example, if you say a sequence and have your kid repeat it back to you, vary the speed at which you talk on different days and don’t just use one class of symbols in your exercises.