Two sequences of activities were developed to provide instruction on the algorithms for addition and subtraction of two-digit numbers. In the integrated sequence (I) the mechanics of "carrying" and "borrowing" were treated as a single process "regrouping." In the sequential treatment (S) the addition algorithm was developed before the subtraction algorithm. Students of two second-grade classes were randomly reassigned to either group S or group I. Profiles were generated by item sampling. Group means were estimated for addition, subtraction and total performance every three days. Also, on the eighteenth day all children were administered a 20-item achievement test. Overall differences in group performance were not significant. Some differences in performance on operations at specific times were significant and favored group S. (A slightly different prepublication draft of this document was announced as ED 062 195.) (Author/MM)