Polanco's D at SS is not AA ready. Why send him up there to boot balls around? His valve as a SS is extraordinarily high. If he is able to master the SS position, he will become a top 20 MLB prospect. If he can't he is probably in the Top 50 range. I say, keep him at High A and let him work on his D while continuing to feast on High A pitching. If he can't cut it there defensively, send him up to AA as a second baseman.