The relationship between K-ABC simultaneous and sequential scores and achievement in reading and math was investigated. Four of the K-ABC simultaneous tests that are nonverbal and two sequential tests were chosen, in addition to a new verbal simultaneous test. Subjects were 79 Grade 5 students. The relationship to school achievement was as follows: (1) a high simultaneous processing score was associated with reading decoding, comprehension, and math scores as obtained from the school records; (2) a high sequential score also was associated with comprehension and math; (3) multiple regression analyses showed a strong predictability of achievement by the simultaneous tests. By far the strongest predictor for reading was the new verbal simultaneous test. Use of this new test with the K-ABC simultaneous tests was recommended. It also was suggested that the predictability of achievement from processing tests may change as processing demands of achievement tests at higher or lower grades change.