Reported are data from the second individual interview conducted in 1979 as part of a 3-year study on addition and subtraction using verbal problem solving. From three schools in Wisconsin that used the Developing Mathematical Processes program, l50 first-grade children were individually administered six problem types (two solvable by addition and four solvable by subtraction) given under four conditions involving size of number and presence or absence of manipulative materials. Answers were coded by model, correctness, and strategy. Discussed first are individual student profiles, followed by a summary of behaviors by task and level. Levels of difficulty, the comparative difficulty of addition and subtraction, the similarity of response patterns for the two addition tasks, subtraction strategies and problem structure, mental strategies, less frequently occurring strategies, and errors are each discussed. Finally, secondary analyses of data are presented. Appendices contain sample problem tasks and individual student profiles. (MNS)