From the perspective of a practicing school psychologist, I would never simply use the highest score and leave it at that when estimating a student's cognitive potential. In the case of significant and unusual discrepancies between Index scores on the Wechsler scales, I would report all of the Index scores and the FSIQ with the caveat that the discrepancies render little utility to the composite score. The same applies when a GAI is calculated, if there is significant and unusual discrepancy between the VCI and PRI. I would then follow up with additional assessments to find out the underlying reason for the discrepancy.
