While the KeyMath is a good comprehensive math assessment, it will not give grade equivalents that are any better psychometrically than the WIAT and WJ, which he has already had. All three tests generate normative data, not true grade placement information. The KeyMath will point out specific skill deficits or peaks, but will not tell you where in the curriculum he should be instructed. For that, you need curriculum-based assessment, using summative (end of unit) and formative (progress monitoring and pretesting) assessments from the curriculum itself.


...pronounced like the long vowel and first letter of the alphabet...