My son is now in 8th grade. Had similar issues with skimming and not following the directions. Found out he would look at the problem without the directions and proceed with his own answer. He also needed to be challenged at an even higher level.
In 5th grade he could comprehend order of operations. Teacher suggested going online for practice. My son picked college level samples with much more difficult equations. Once he mastered those practice problem he told me the ones at school were too easy...he thought they needed more steps. Apparently he was overcomplicating the process because the 5th grade work was too boring. He is now in 8th Grade, doing similar problems and moving through the work faster than the teacher can give him new assignments. We are looking into switching to a private school that will let him chose the course level of Math he wants to learn instead of having to be bored with something he has known since 5h grade. By the way, the 8th Grade class he is in now is suppose to be an AP Alegbra course.
By the way, back to the original question...does you child have any speech or reading allow issues. In first grade my son was put into Speech for fluency issues. They claimed at the time that his speech was effected by his intellegence being higher than his physical development. He was frustrated that he couldn't communiticate as fast as he could function mentally. Does that sound familar to anyone else?