It may be because the board attracts a high % of kids who are 2E or 2E-ish, or who are clearly gifted but not fitting into the school "box" all that well. My DD didn't take an IQ test that measured WM, but hers is clearly very good (I posted in another thread about her digit span, which is better than mine). She's also (so far) cruising through school at a gifted magnet.