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• A Lesson from Forrest Gump Regarding Expectations for Students with Cognitive Disabilities

Kevin S. McGrew, PhD

Director

Institute for Applied

Psychometrics (IAP)llc

Visiting Professor

Educational Psychology

University of Minnesota

www.iapsych.com

2. Mrs. Gump: Well, we're all different, Mr. Hancock.He might be a bit on the slow side.He's not going to a special school toretreadtires ! Principal: Your boy's... different, Miz Gump. His IQ's 75. 3. As we all know, Forrest accomplished a lot --- much more than his IQ score would have suggested.How can this be ? Sometimes there justarent enough rocks 4. Lets get an empirical answer from a national norm sample the Woodcock-Johnson Battery-Third Edition (Woodcock, McGrew & Mather, 2001; WJ III) What should our expectations be for Forrest in reading? 5. What should our expectations be for Forrest in reading? 40 50 60 70 80 90 100 110 120 130 140 150 160 IQ=75+5 Forrest Gumps score 6. WJ III GIA SS 70-80 (in the norm data) What should our expectations be for Forrest in reading? 40 50 60 70 80 90 100 110 120 130 140 7. Ability/AchievementRelations Reuire Adjusting for Regression to the Mean This model reflects the less than perfect correlation between ability and achievement measures Ability Achievement 100 115 130 85 70 100 115 130 85 70 8. 90 100 110 120 130 140 40 50 60 70 80 Expected Basic Rdg Skills SS (for GIA SS = 70-80 )???? WJ III GIA SS 70-80 (in the norm data ) Must first account for regression to the mean 9. 90 100 110 120 130 140 BRS 40 50 60 70 80 Basic Rdg Skills SS (for GIA SS = 70-80 ) Where will most of the Forrest Gumps of the world achieve in reading? Regression-based expected score 10. Intelligence tests:Quantoid fact 1

For any given IQ score:

• Halfof the students will obtain achievement scores at or below their IQ score.

• Halfof the students will obtain achievement scoresat orabove their IQ score !

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IQ test scores, under optimal test conditions, account for 40 % to 50% of current expected achievement

Thus, 50% to 60 % of student achievement is related to variables beyond intelligence

Intelligence tests:Quantoid fact 2 12. The relationship between intelligence and achievement in a nationally representative sample these are REAL subjects WJ III Battery norm data (see McGrew & Woodcock, 2001) WJ III General Intellectual Ability WJ III Total Achievement IQ-ACH correlation = .75 Note the normal curve shape of both the IQ and Ach distributions 13. The relationship between intelligence and achievement in a nationally representative sample these are REAL subjects The tighter the spread of the individual data points (ideally along a single line cutting through the middle of the plot) the more accurate the prediction of achievement will be based on IQ. The amount of spread around the line represents the amount of error when trying to make a prediction based on IQ.Technically it is called thestandard error of estimate .WJ III General Intellectual Ability WJ III Total Achievement IQ-ACH correlation = .75 14. The relationship between intelligence and achievement in a nationally representative sample these are REAL subjects The tighter the spread of the individual data points (ideally along a single line cutting through the middle of the plot) the more accurate the prediction of achievement will be based on IQ. The amount of spread around the line represents the amount of error when trying to make a prediction based on IQ.Technically it is called thestandard error of estimate .WJ III General Intellectual Ability WJ III Total Achievement IQ-ACH correlation = .75 15. WJ III General Intellectual Ability WJ III Total Achievement IQ-ACH correlation = .75

Lets pull a slice of the data points out for closer inspection.

Lets select all subjects withIQ scores between 70 and 80.

What will their achievementscores look like?

Will their achievement scores be