This study was conducted with the purpose of examining how Prospective Science Teachers' (PST) Science Process Skills (SPS) develop according to different grades. In this study, a cross-sectional research approach in the form of a case study was used. The sample group consisted of a total number of 102 undergraduate students who were selected from four different grades [(First Grade = Freshman) N=33; (Second Grade = Sophomores) N= 23; (Third Grade = Juniors) N= 27; (Fourth Grade = Seniors) N= 34] at the Department of Science Teacher Education, in the Faculty of Education, the University of Giresun. As the data collection tool, a test of assessing science process skills included 12 questions (9 multiple choice and 3 open ended questions) was used in this study. The mean SPS scores for students from different grades were compared. Kruskall-Wallis H test was used to determine whether or not there were significant differences in the levels of the different grades PST' SPS. Although PST were expected to develop their SPS over the increasing grade levels from the first to the fourth grade, the findings of this study show that there is no linear development. (Contains 6 graphs and 6 tables.)