Physical science is important for developing scientific literacy yet a majority of teachers responsible for physical science courses do not have an academic degree in physical science. Programs aimed at increasing teacher content knowledge can be time consuming. This dissertation examines the impact of an inquiry based, professional development program offered via distance learning on teacher content knowledge and the role of teacher content knowledge on student understanding and attitudes toward science. Seventy-three teachers participated in the study, including Group I teachers (n = 39) who completed a distance learning course, a control group (Group II) with no intervention (n = 17), and Group III teachers (n = 17) who received classroom materials and no course intervention. A multiple-choice assessment was administered to teachers at the beginning and end of the summer. A similar multiple-choice assessment was administered during the school year to students (n = 3,790) of those teachers. A teacher survey assessing the frequency of activity use and teachers' perceptions of the kit was administered to teachers at the end of the school year. A student survey assessing frequency of activities in the classroom, opinions of how to learn science, and attitudes toward science was administered to students during the school year. While Group II (50.6%) and Group III (52.2%) teacher scores were both lower than Group I teacher scores (67.4%), students in Group III (42.9%) outperformed students in Group II (39.4%) following instruction, at a level equal to Group I students (43.6%). Thus, providing materials/activities was as effective at increasing student understanding as providing materials/activities and increasing teacher understanding. However, while teachers in Group I and III report similar use of and satisfaction with the materials/activities, the percentage of Group I students reporting frequent use of inquiry based activities in the classroom, strong belief that inquiry based activities help them learn science, and positive attitudes toward science increased, while the percentages of students in Groups II and III decreased. These results suggest that in order to maximize students' understanding of and attitudes toward science, professional development programs should not only include inquiry pedagogy and laboratory materials but also emphasize teacher understanding. [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://www.proquest.com/en-US/products/dissertations/individuals.shtml.]