Strategies used by 15 fifth and sixth grade students to comprehend written problem solving tasks were identified. A naturalistic protocol analysis procedure was used to gather and analyze students' verbal and written responses to 55 selected reading and thinking tasks. In the ten tasks selected for detailed analysis, students demonstrated marked differences in their use of four principal strategies: visualization, experimentation, abstraction, and extension. Analysis of incorrect responses generated three principal categories of errors: "perplexed responses,""literally bound responses," and "attempted experimentation." The results of this investigation provide further description of the process of transition from concrete to formal operations occurring during early adolescence and suggest implications for curricular planning and reading instruction for middle school students. (Author/BW)