All students receive a standardized score on a common vertical scale which reveals how the tested students performed in comparison to grade-specific national norms. Such standard scores are known for all grades.
A percentile rank tells what percentage of students in a specific group received lower scores than the student in question. The range is from 1-99.
Each student's score corresponds to a percentile relative to the distribution of other students' scores in the same grade, for a particular month. The percentage of scores at or below a particular value defines scores' percentiles.
Students with score percentiles near 50 are at the average for the month in which the assessment was taken. Lower percentiles indicate slower overall growth, while higher values indicate accelerated overall growth relative to the nation at large.
The table below shows the Scale Scores at the 10th, 50th, and 90th percentile for grades K-8 in the months of September, January, and May: