You raise an interesting point, Cynthia. You raise the question of how many students have been identified as learning disabled because of ineffective instruction (be it math, English, history, etc). I looked at this question in the article here.
This site uses left-brain and right-brainnot as physiological terms for the actual left and right hemispheres of the brain, but as they are employed in the everyday vernacular. They appear here in the same spirit in which people use type A and type B (themselves the relics of a debunked theory about blood type and character type): an informal shorthand for certain bundles of personality traits.