That's what doesn't make very much sense to me. Here... I will paste in a very quotes from their web site.
Grade equivalents are particularly useful and convenient for measuring individual growth from one year to the next and for estimating a student's developmental status in terms of grade level. But GEs have been criticized because they are sometimes misused or are thought to be easily misinterpreted. One point of confusion involves the issue of whether the GE indicates the grade level in which a student should be placed. For example, if a fourth-grade student earns a GE of 6.2 on a fourth-grade reading test, should she be moved to the sixth grade? Obviously the student's developmental level in reading is high relative to her fourth-grade peers, but the test results supply no information about how she would handle the material normally read by students in the early months of sixth grade.
Developmental Standard Score (SS)
Like the grade equivalent (GE), the developmental standard score is also a number that describes a student's location on an achievement continuum. The scale used with the ITBS and ITED was established by assigning a score of 200 to the median performance of students in the spring of grade 4 and 250 to the median performance of students in the spring of grade 8.
The main drawback to interpreting developmental standard scores is that they have no built-in meaning. Unlike grade equivalents, for example, which build grade level into the score, developmental standard scores are unfamiliar to most educators, parents, and students. To interpret the SS, the values associated with typical performance in each grade must be used as reference points.
So they seem to indicate that a child could earn above grade level scores on the IBSt, and they scale the scores in a continuum. So for instance, DS(then 6) scored a 200 in vocabulary at the very beginning of 1st grade. Does that mean that he had a score of an average 4th grader?
