The scaling approach taken by the DC CAS is, to my mind, pretty unconventional, because the scaled scores do not overlap across grades. In grade four, the minimum possible scaled score is 400, and the maximum possible scaled score is 499. In grade five, however, the minimum possible scaled score is 500, and the maximum possible scaled score is 599. (The same approach is used in grades six through eight.)
This means that a fourth-grade student who got every question on the fourth-grade math assessment correct would receive a lower scaled score than a fifth-grade student who got every question wrong on the fifth-grade assessment.
That sounds ridiculous, but it’s not problematic if the scale for fourth-grade performance is acknowledged to be different from the scale for fifth-grade performance. The design of the DC CAS allows for comparing performance in fourth grade in one year with fourth-grade performance in the next year; but it doesn’t permit measuring how much students have gained from one grade to the next. Measuring growth from one grade to the next requires a test that is vertically equated.