It surely helps. Take for example History, if I space out for whatever reason in the class and botch my examination on the Aztecs, that doesn't preclude me doing great in the classes about the Roman empire. History is like a sparse suburb, where a single house catching fire does not necessarily propagate and destroy the others. On the other side Math its like a skyscrapper, one floor build upon the other. If someone living in a lower floor botches a home renovation in his unit and damages a pillar, it risks taking down the whole building. In math if you botch a prerequisite, you'll ending messing your learning of subsequent concepts 95% of the time. So it is more unforgiving to people with problems like ADHD, that struggle to keep unbroken focus and discipline.