A severe discrepancy exists when the difference between a student's measured ability and academic achievement is greater than 1.5 standard deviation units. The district’s procedure uses the ability and achievement tests which yield standard scores based on a mean of 100 and a standard deviation of approximately 15. Accordingly, a severe discrepancy exists if a student's achievement test score is 22 or more standard score units below the student's ability test score using the full scale intelligent quotient in one or more of the following academic areas: