As part of a 3-year study of arithmetic problem-solving skills in young children, pretests were administered to 180 middle class first grade students. Following each of three instructional units, another achievement test was administered. The three first grade units corresponded to the Developing Mathematical Processes curriculum and involved mathematical sentence writing. The goal of the set of 10 instructional units, to be conducted over the 3-year period, was for children to develop efficient problem-solving behavior in addition and subtraction problem situations. Skills leading to this behavior were the ability to symbolize verbal problems in the form of written addition or subtraction sentences, to retrieve addition and subtraction facts, and to use addition and subtraction algorithms. Mastery of each of the instructional objectives was expected at definite times during the sequence. Matrix sampling was used to divide students into three test groups; test reliability was acceptable in all three groups and difficulty equivalent. Results indicated that students demonstrated mastery of all prerequisite instructional objectives and made satisfactory progress on the instructional topics. (Over half of this document contains sample test items, testing instructions, and item statistics.) (GDC)