Researchers separate two kinds of effects. Near transfer means skills that share parts with the thing you practised, for example working memory, processing speed and coordination of the hands. Far transfer means things that look unrelated, like mathematics or general intelligence.
What the reviews say
Reviews of music training have found some near transfer and little reliable evidence of far transfer. In other words, piano can sharpen the skills it uses. It is not a shortcut to being cleverer.
What the benefits depend on
The changes come from the demands of the activity: reading music, listening, and coordinating two hands in real time. They do not depend on how well it sounds. A slow, imperfect play-through counts.
Why we build iCanPiano the way we do
The less you fight with the page, the more of your attention goes to listening and moving. In iCanPiano Style a note played on a black key shows it every time, so there is no key signature to work out before each note. This is a design choice, not a research result: we have not measured brain effects of the method.
Frequently asked questions
Does piano improve maths?
Reviews of music training have not found reliable improvement in unrelated skills such as maths.
What does piano improve, then?
Skills close to what you practise: working memory, speed, hand coordination and, in some trials, verbal fluency and flexibility.
Is it still worth learning piano?
Yes, for the music and the enjoyment. The brain effects are a modest bonus, not the main reason.