Using Percentiles to Determine General Areas of Strengths and Needs

What is a percentile?

A percentile is a norm-referenced, derived test score that ranges from a low of 1 to a high of 99. For each subtest and grade level, the national median percentile is 50. (The media score of a set of ranked scores is the score which separates the set of scores in half.) Therefore, at the national level, one-half of the scores are above the 50th percentile and one-half are below the 50th percentile.

 

How are percentiles interpreted?

Percentiles compare a student's or a group's relative standing within a comparison or reference group. For national percentiles, the comparison group is the national group on which the test was normed. For example, a fourth grade student who earned a national percentile of 76 scored as a high or higher than 76% of the fourth graders in the national norm group. Also, 24% (100-76) of the fourth graders in the national norm group scored higher than the student did. A group's median national percentile of 35 means that 50% of the group scored above the 35th percentile and 50% scored below the 35th percentile. In the national group, only 35% of the students were below the 35th percentile and 65% were above the 35th percentile.

 

How are percentiles used?

Percentiles may be used to determine a student's or a group's relative (compared to the national group) strengths and weaknesses from one subtest to another. For example, if a student earned a percentile of 82 on the Mathematics subtest and a percentile of 47 in Reading, it is appropriate to conclude that, relative to the national group, the student performed better in Mathematics than in Reading. The student was above average (above the 75th percentile) in Mathematics, but about average (near the 50th percentile) in Reading. In general, percentiles are not used to show growth from year to year. For example, if a student's national percentile on the Science subtest is 50 in the 4th grade and 50 in the 5th grade, it is inappropriate to conclude that the student made no growth in Science from 4th to 5th grade. In fact, by maintaining his average standing from the 4th to the 5th grade, the student grew in Science achievement at an average rate. In the 4th grade, the student scored as well as or better than 50% of the 4th graders. The next year he also scored as well as or better than 50% of the 5th graders. Because percentiles are not based on an equal-interval scale, they may not be used in mathematical calculations. For example, it is incorrect to average a Reading percentile of 40 with a Vocabulary percentile of 50 to yield a Reading Composite percentile of 45.

 

On which reports are percentiles found?

Percentiles for individual students are found on the reports entitled Individual Profile Report and Class Record Sheet. Median national percentiles (abbreviated MDNP) for a teacher's class are provided on the Class Record Sheet. MDNPs for a grade level within a school or district are found on the Class Summary Report.

 

Step One-

Record your class/subject scores from the Class Summary Report onto the TCAP Median National Percentiles Chart for the years 1998-2002. Compare the scores from the past 5 years. Determine if and how your class has changed.

Step Two-

Record your findings on the "Interpreting Your Groups MDNP" sheet. Use this information to identify areas of strength and or weakness.

 

 

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