This study investigated the rates of successful mathematical performance and errors of information processing in third-grade children in California and continued an investigation of these factors in sixth-grade children. The objectives were to: (1) identify areas of mathematics in which the children had recognizable strengths and weaknesses, (2) classify characteristic areas according to information-processing theory, and (3) relate the errors made by third graders in l980 with errors made by the same children as sixth graders in l983. Approximately 25,000 children in each grade were tested for each year using data from the Survey of Basic Skills in the California Assessment Program. The tests and population are first briefly discussed, followed by the results of the analyses. For each grade level, discussion focuses on: correct performance by categories --computation, counting/number property, word problems (using operations), visual problems, geometry/measurement problems, and nontraditional story problems; the most difficult items; scores on matched items (computation and applications); and errors. Then the longitudinal analysis is dicussed. Girls appear stronger than boys in grade 3 and boys were stronger than girls in grade 6. References and sample items are included in the appendix. (MNS)