A Solomon Four-Group research design was used to investigate the effectiveness of the Selective Problem Solving Model (SPS) on the development of students' creativity skills in mathematics. The SPS is a highly structured creative problem solving model composed of six steps. The participants of the study included 201 seventh-grade students who were attending a public school. As the principles of the Solomon Four-Group research design, the study included eight classrooms randomly assigned to two experimental and two control groups. A total of 10 SPS lesson plans were developed and used in four experimental classrooms. No intervention was carried out in the control classrooms. The Analogical Problem Construction Test and the Problem Analysis Test were used as the pre-tests and post-tests to measure analogical problem construction and problem analysis skills in mathematics. The findings showed that the experimental groups had significantly higher gain scores than the control groups. Additionally, the experimental groups had higher post-test scores on both measures than did the control groups. The findings can be interpreted that the SPS Model improves students' creativity skills in mathematics.