This study was designed to compare the effectiveness of using traditional and integrated instructional strategies to increase student understanding of the core concepts of energy. There are mixed messages in the literature as to the success of using an integrated approach to teach science content, despite suggestions its use improves student achievement and attitudes toward science. This study used a mixed-method approach. The quantitative portion was a quasi-experimental non-equivalent control group design, and the qualitative portion included teacher journals, teacher interviews and student journals. There were three teacher participants, two in the treatment group from a district in Sussex County, Delaware. The third teacher participant, from a different district in Sussex County, Delaware was in the control group. The treatment group consisted of 180 students and the control group consisted of 124 students. The results of this study show that the treatment group had significantly less anxiety in science following the treatment, than students in the control group. The F value of 10.89 was significant at p = 0.001. Students in the treatment group also had more enjoyment of and motivation in science than did students in the control group. The F value of 25.025 was significant at a p = 0.000 for the subscale enjoyment of science. The F value of 14.1 was significant at a p = 0.000 for the subscale of motivation in science. Students in the treatment group performed significantly better on the achievement tests, the Integrated Summative Energy Assessment (ISEA) and the science portion of the Delaware State Testing Program (DSTP). The treatment group performed significantly better on the ISEA than did the control group, with an F value of 407.7 significant at p = 0.000. The treatment group performed significantly better on the science DSTP than the control group, with an F value of 65.81 which was significant at p = 0.000. The use of an integrated approach to science instruction decreases student anxiety, increases enjoyment of science and motivation in science more than a traditional approach to teaching science. The use of an integrated approach to science instruction increases student achievement on extended response assessments that measure integrated conceptual knowledge and increases student achievement on traditional summative assessments. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]