Standardized tests, (probably due to all of that standardization) can be hard to understand. Knowing what your child's score is doesn't necessarily tell you what it means. Here's some insight. Most tests used in schools today are one of two types: either norm-referenced or criterion-referenced tests.
Norm-referenced tests are graded by comparing the tester's performance with that of the other students taking the test. It provides information on how a child does in relation to his peers, but does not indicate what a child does or does not know. Norm-referenced tests are often scored in one of several ways: percentiles (in which a percentage indicates the percentage of test takers the individual did as well as or better than), stanines (rarely used today, these are basically groups of percentile ranks), standard scores (standard scores indicate how far above or below the average score a student performed) and age/grade equivalent scores (these scores indicate how the student did in comparison to the expected score of his age or grade group).
These scores indicate the level of a student's mastery of material or curriculum. Scores are often presented as a percentile that represents the percentage of questions a student got correct out of all the questions on the test.
To learn more about test scores and types of standardized tests click here.