A Z score (also known as a z value, standard score, and normal score) is used to describe a particular score in terms of where it fits into an overall group of scores. In other words, a Z score is an ordinary score transformed so that it better describes the location of that score in a distribution. A Z score has a mean of zero and a standard deviation of one.
T scores are used to tell individuals how far their score is from the mean. T scores have a mean of 50 and a standard deviation of 10. Therefore, if a student’s raw score was converted to a T score and their T score was 70 it would in turn mean that their score was 20 points above the mean. One advantage of using a T score over a z score is that T scores are relatively easy to explain to parents when reporting the student’s assessment scores.