Hello I would like you to motivate child with rewards rather than punitive measures. Just discuss with him prior to task how he wants to do it and how it is to be done. Make multistep in a single task and reward him after each step achieved successfully. I would like you to take help of professional for cognitive behavioural therapy. Learning disability and ADHD are two different things. Every learning disability is not ADHD. ADHD can itself lead to learning disability. In both conditions if treated properly children with these conditions can excel in any profession including engineering, law and medicine. So in treatment parents do have major role to play. So I would like you to take professional help in this regard and help your child to shape his future.