Developing students' creative problem solving skills should be one of the top goals in general education. One teaching model that was developed to increase students' creative problem solving abilities is the Real Engagement in Active Problem Solving (REAPS) model. This model was used as an intervention in classrooms in many studies. However, the researchers of these studies did not examine the relationship between the levels of implementation of this model and its effect on students' creativity in science. In the current study, the author aimed to determine the influence of the level of fidelity of implementation (FOI) of the REAPS model on creative problem solving in science. Specifically, the purpose was to examine the relationships between changes in students' growth in creative problem solving in science and the level of FOI of the REAPS model. A quasi-experiment design was used, and the study took place in one elementary public school in Australia for two years. The total number of students who participated was 317. In Year 1, the number of classrooms was 17, and students were in grade 2 to 5. In Year 2, the number of classes was 16, and students were in grades 3 through 6. The instrument used to collect data was the Test of Creative Problem Solving in Science (TCPS-S). Students took a pretest prior to exposure to REAPS in Year 1, and they took a posttest at the end of Year 2. One-Way Repeated Measures Multivariate Analysis of Variance (MANOVA) was used to answer the three research questions. Five dependent variables were used in Questions 1 and 2: the total scores on TCPS-S, fluency, flexibility, elaboration, and originality. Grade levels were used as an independent variable for Question 1, and levels of FOI were used as an independent variable for Question 2. For Question 3, three dependent variables were used: Finding Problems, Generating Detailed Solutions, and Classifying Elements with one independent variable: levels of FOI. In general, students showed growth in their science creativity scores from pretest to posttest. Lower grade students showed growth on originality, which was statistically significant, compared with students in upper grades (i.e., grades 4 to 6), while the upper grade students showed growth on the total scores on TCPS-S, fluency, flexibility, and elaboration, which was statistically significant. Students who were with high implementers for two consecutive years or with high implementers in the second year showed growth on flexibility and elaboration, which was statistically significant, compared with students who were with low implementers for two years or with low implementers in the second year. No differences were found among the levels of FOI on the total scores on TCPS-S, fluency, and originality. Students who were with high implementers for two consecutive years or with high implementers in the second year showed growth in their scores in two factors of TCPS-S: Generating Detailed Solutions and Classifying Elements. However, no differences were found in Finding Problems factor among the levels of FOI. Future research is recommended to examine the effects of the use of REAPS on students' creativity in different disciplines. [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.]