The primary purpose of this study was to compare regular classroom instruction which used Guided Mental Imagery (GMI) to a non-GMI teaching method. This comparison was expected to yield data which would provide insights relating to the potential of GMI as a useful and effective instructional strategy. Quasi-experimental research methods were followed. The experimental design was a modified "post-test only control group design." Two-hundred-four students in naturally occurring in tact classes formed the experimental and control groups. All groups received instruction in identical science/health content. Two parallel post-tests were administered to all students. Post-test "A" was given immediately after instruction to measure learning acquisition. Post-test "B" was given four weeks later to measure retention of learning. Means for test scores were grouped according to treatment and sub-grouped by the variables: IQ, handedness, identified learning disability, and intellectual giftedness. T_ tests for differences between independent means were conducted. Students' acquisition of basic academic content, when instructed with GMI methodology, was found to differ significantly from students' acquisition of the same content with non-GMI instruction. No statistically significant differences based on instructional methodology were found for content retention. The investigator concluded that GMI instruction may increase learning. Although measures of retention did not show significant differences between groups, a review of the mean scores revealed a minimal difference. This was interpreted to indicate equality of retention between the two methods. Recommendations for further investigation were offered. Post-testing of subjects at additional intervals, and increased training of students and teachers in GMI prior to collection of data were suggested.