This study assesses the adequacy of item gradients and ceilings for the subtests of the Woodcock-Johnson III (WJ III) Cognitive and Achievement batteries, including the Diagnostic Supplement, in their use with participants ages 16 to 25 and Grades 10 to 18. Of the 52 subtests, 18 contain adequate item gradients and ceilings for the entire age and grade range. The remaining 34 subtests have inadequate ceilings and/or inadequate item gradients in at least the interval between the first and second standard deviations above the mean, as predicted by the growth curves of the factor clusters, which peak around age 25. The report discusses developmental and practical implications and suggests improvements for the next revision of the WJ. (Contains 3 tables.)