The two main things to know are:
We cover these two items below (and more - just to be thorough).
Note that the Iowa test scores are NOT of the type where 90-100% is an "A", 80-89% is a "B", etc. In the Iowa Tests, 50 percentile is average. There is no "A" or "B"; no "passing grade" or "failing grade". In the chart below, you can see this demonstrated somewhat. The public schools are "average".
Three of the fundamental purposes for testing are:
To accomplish any one of these purposes, it is important to select the type of score from among those reported that will permit the proper interpretation. Scores such as percentile ranks, grade equivalents, and standard scores differ from one another in the purposes they can serve, the precision with which they describe achievement, and the kind of information they provide. All test scores, no matter which type they are or which test they are from, are subject to misinterpretation and misuse. All have limitations or weaknesses that are exaggerated through improper score use. The key is to choose the type of score that will most appropriately allow you to accomplish your purposes for testing.
Types of Scores
Percentile Rank (PR)
Percentile Rank is the big score to pay attention to - the one that reflects performance. This is the score used to "compare" homeschooler effectiveness - by the legislature and others. It's the one used in the chart above. Most people look at this score and stop here - ignoring the other scores.
A student's percentile rank is a score that tells the percent of students in a particular group that got lower raw scores on a test than the student did. It shows the student's relative position or rank in a group of students who are in the same grade and who were tested at the same time of year (fall, midyear, or spring) as the student. Thus, for example, if your child earned a percentile rank of 72 on the Language test, it means that she scored higher than 72 percent of the students in the group with which she is being compared. Of course, it also means that 28 percent of the group scored higher. Percentile ranks range from 1 to 99.
A student's percentile rank can vary depending on which group is used to determine the ranking. A student is simultaneously a member of many different groups: all students in her classroom, her building, her school district, her state, and the nation. Different sets of percentile ranks are available with the Iowa Tests of Basic Skills to permit schools to make the most relevant comparisons involving their students.
Raw Score (RS)
The number of questions a student gets right on a test is the student's raw score (assuming each question is worth one point). By itself, a raw score has little or no meaning. The meaning depends on how many questions are on the test and how hard or easy the questions are.
Percent Correct (PC)
When the raw score is divided by the total number of questions and the result is multiplied by 100, the percent-correct score is obtained. Like raw scores, percent-correct scores have little meaning by themselves. They tell what percent of the questions a student got right on a test, but unless we know something about the overall difficulty of the test, this information is not very helpful. Percent-correct scores are sometimes incorrectly interpreted as percentile ranks, which are described below. The two are quite different.
Grade Equivalent (GE)
The grade equivalent is a number that describes a student's location on an achievement continuum. The continuum is a number line that describes the lowest level of knowledge or skill on one end (lowest numbers) and the highest level of development on the other end (highest numbers). The GE is a decimal number that describes performance in terms of grade level and months. For example, if a sixth-grade student obtains a GE of 8.4 on the Vocabulary test, his score is like the one a typical student finishing the fourth month of eighth grade would likely get on the Vocabulary test. The GE of a given raw score on any test indicates the grade level at which the typical student makes this raw score. The digits to the left of the decimal point represent the grade and those to the right represent the month within that grade.
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. Thus, the GE only estimates a student's developmental level; it does not provide a prescription for grade placement. A GE that is much higher or lower than the student's grade level is mainly a sign of exceptional performance.
Grade equivalents are particularly suited to estimating a student's developmental status or year-to-year growth. They are particularly ill-suited to identifying a student's standing within a group or to diagnosing areas of relative strength and weakness.
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.
The main advantage of the developmental standard score scale is that it mirrors reality better than the grade-equivalent scale. That is, it shows that year-to-year growth is usually not as great at the upper grades as it is at the lower grades. Despite this advantage, the developmental standard scores are much more difficult to interpret than grade equivalents. Consequently, when teachers and counselors wish to estimate a student's annual growth or current developmental level, grade equivalents are the scores of choice.
Interpreting Scores from Special Test Administrations
A testing accommodation is a change in the procedures for administering the test that is intended to neutralize, as much as possible, the effect of the student's disability on the assessment process. The intent is to remove the effect of the disability(ies), to the extent possible, so that the student is assessed on equal footing with all other students. In other words, the score reflects what the student knows, not merely what the student's disabilities allow him/her to show.
The expectation is that the accommodation will cancel the disadvantage associated with the student's disability. This is the basis for choosing the type and amount of accommodation to be given to a student. Sometimes the accommodation won't help quite enough, sometimes it might help a little too much, and sometimes it will be just right. The use of an accommodation should help the student experience the same conditions as those in the norm group. Thus, the norms still offer a useful comparison; the scores can be interpreted in the same way as the scores of a student who needs no accommodations.
A test modification involves changing the assessment itself so that the tasks or questions presented are different from those used in the regular assessment. A Braille version of a test modifies the questions just like a translation to another language might. Helping students with word meanings, translating words to a native language, or eliminating parts of a test from scoring are further examples of modifications. In such cases, the published test norms are not appropriate to use. These are not accommodations. With modifications, the percentile ranks or grade equivalents should not be interpreted in the same way as they would be had no modifications been made.
Certain other kinds of changes in the tests or their presentation may result in measuring a different trait than was originally intended. For example, when a reading test is read to the student, we obtain a measure of how well the student listens rather than how well he/she reads. Or if the student is allowed to use a calculator on a math estimation test, you obtain a measure of computation ability with a calculator rather than a measure of the student's ability to do mental arithmetic. Obviously in these situations, there are no norms available and the scores are quite limited in value. Consequently, these particular changes should not be made.