This study involved the extensive testing and interviewing of 102 primary grade pupils, representing a sampling from diverse school environments, to study the capabilities and difficulties evidenced by primary-grade pupils in solving open addition and subtraction sentences. Phase 1 of the study identified the specific incorrect procedures commonly used by pupils in completing such sentences. Since the major incorrect procedures were analyzed as representing difficulties in reading number sentences correctly and with understanding, Phase 2 investigated the importance of (a) reading such sentences and (b) being able to demonstrate their meaning with manipulatives as determiners of ability to solve them. (Author/MN)