We hypothesized that computer tools that provide models, opportunity for higher level thinking, and metacognitivelike guidance (e.g., "Can I conjure up an image of the story?") can serve in a learner's zone of proximal development (Vygotsky, 1978); they can develop competencies through internalization. A computerized Reading Partner presented four reading principles and metacognitivelike questions during the reading of 11 texts over three reading sessions. It was compared with one version that presented the texts with factual and inferential questions and a control version that presented only the texts. Seventh graders using the Reading Partner (n = 25) reported the expenditure of more mental effort in the process, showed far better metacognitive reconstruction, and improved significantly more in their later reading comprehension and in the quality of their written essays than did the subjects in the other groups. Improvements in reading and writing were statistically accounted for by subjects' ability for metacognitive reconstruction. The study reinforces previous findings pertaining to the role of metacognitions in reading and shows that well-designed computer tools can cultivate competence.Computer tools, unlike drill and practice programs, have been argued to serve as "cognitive tools" (e.g., Pea, 1987) that can help the development of thinking skills (Pea, 1985). However, little empirical study has been devoted to these possibilities. This study, based mainly on Vygotsky's (1978) sociodevelopmental theory, was designed to test hypotheses about the effects of a computer tool on the cultivation of students' reading-related metacognitions. The latter were conceptualized as readers' self-regulation of their thinking while reading, that is, "the monitoring and redirection of one's activities during the course of reading to reach the desired goals" (Cross & Paris, 1988, p. 131). Examples of such metacognitions are one's self-regulated summaries of a text or one's deliberate attempts to identify key sentences.According to Vygotsky (1978), social interaction, including instruction, serves as a major force in the growth of human competence. Specifically, thinking has its basis in a social activity that becomes internalized. It follows, then, that guided social interactions, which initially serve as instruments for social regulation and communication, gradually come to serve a cognitive function for self-regulation and for mental representation of information. These interactions activate not yet fully developed cognitive functions that allow the learner to perform on a higher cognitive level. However, these higher The research reported here was supported by a Spencer Foundation grant given jointly to Gavriel Salomon and to Tamar Globerson. While this article was in its final stages of preparation, Tamar Globerson met a sudden and untimely death.