Hmm - it's unfortunate that your DS' school used the Terra Nova for achievement. My recollection is that there is not a whole lot of headroom. DS16, who took it almost a decade ago in 2nd grade, scored 99 percentile by missing only 1 or 2 questions. In other words, any tendency toward carelessness could significantly drop your score. I think that you can make a good argument with excellent achievement scores with a much higher ceiling.