You'd have to contact ITBS or find someone who has tested a 1st grader. I can tell you from my 3rd grader. The percentiles drop quickly depending on the subtest. Generally, percentile drops about 4-5 points for each missed point. I'm not sure if this is linear or not however. For example, Vocabulary 28/29 correct yields 96th%. 27/29 correct and it's 96th% whereas for science 29/30 yields 99th% and 28/30 yields 98th%. For usage and expression, missing 5 gets you 76th%. In math, missing 7 out of 25 questions can drop you to 63% quickly.
1%-9% is weak; 10%-40% is below avg; 41%-89% is average; 90%-99% is above average.
Is that what you're talking about?
