It not quite as straight forward as that, my children get little to no academics at home either, and don't have the personality / inclination to pursue academic learning for entertainment. But even with how incredibly average I think her classroom placement is, and that she was not much ahead when she started school, and she has ADHD - my almost 7 yr old DYS iq DD is still ripping through academic learning at a pace normal kids don't/can't do. Including moving on very quickly from reversals and learning to compensate for handwriting disability that her OT had thought would be insurmountable. A child that gifted should be rocketing along - unless there is a reason why not (which may not be an LD, but its certainly worth figuring out why they're not).
