The National Council of Teachers of Mathematics encourages the use of calculators in the classroom as a teaching and learning tool, as well as a computational tool. This paper evaluates the impact on teachers' approaches to teaching mathematics and students' attitudes toward mathematics as the result of participation in an in-service program designed to help third and fourth-grade teachers incorporate calculators into their instruction. Forty-two teachers from 14 rural Missouri school districts were invited to participate in three 1-day workshops held in the 1991-92 school year. The teachers were taught to use Texas Instrument Explorer calculators, encouraged to explore numbers and number relationships with the calculators, and asked to design five higher-level lessons to utilize the calculator. Results of a questionnaire used to assess changes in the teachers' (n=29) instructional approaches indicated no significant differences materialized in the teachers' teaching approaches and teachers hold misconceptions about such concepts such as division by zero. Pretest and posttest analysis of the students' (n=412) attitudes toward mathematics indicated that students developed a more positive attitude on scales dealing with value of division, willingness to do division, enjoyment of division, calculator use, and overall perception of mathematics. (MDH)