Although the scores and percentiles are the same in both versions, some people think that the WPPSI scores are over-inflated in that extreme upper end at least. Since you have a barely there score with the achievement, it is tricky. If you continue to see him progressing fast (in essence increasing his separation to his peers in achievement), you could retest in a couple of years.
In the meantime, have you looked at all the articles in the Davidson database? Those will be good parting points for advocacy ideas.
Did you do testing independently or through school? If you did on your own, have you shared his results with his teacher and the principal?
