He could be dyslexic or have a mild form of autism. He may have a brain tumor. He might even be a heavy drinker who has lost some degree of brain function due to the cumulative effects of alcohol. Jack may not even realize that he has a cognitive deficit, but his unsuccessful attempts to follow your teaching may lead you to suspect a cognitive impairment. It involves such skills as remembering, understanding language, handling abstract concepts, following multi-step instructions, and exercising prudent judgment.
Some people associate cognitive deficits with mental retardation.
Although mentally retarded individuals are always cognitively impaired, not all cognitively impaired individuals are mentally retarded. Many may have normal intelligence, but a cognitive impairment may make it difficult to learn new motor patterns. This may be because the student has short-term memory problems, or because he or she cannot translate your words or imitate your movement patterns as a result of an impaired ability to conceptualize. The student may encounter difficulty because your style of presentation is too abstract, too removed from his or her frame of reference. Perhaps the student just doesn't understand the words or ideas you are using, or a disorganized way of thinking prevents him or her from planning motor movements in sequence.