Why do science education programs target particular preservice teacher year levels? Using a 35-item survey, responses from 127 second-year preservice teachers were compared with 164 third-year preservice teachers from the same university within the same year entering the same science education course. The survey, which was linked to the course outcomes and multiple indicators, measured the preservice teachers? perceptions of their prior knowledge before involvement in a primary science education course. Examining the differences between the two cohorts (i.e., n=127 and n=164), results indicated statistically significant t-test scores for each of the four constructs (i.e., Theory [t=6.07], Children?s Development [t=7.85], Planning [t=10.31], Implementation [t=11.10]; p<.001) in favor of the third-year cohort. It is argued that each and every cohort of preservice teachers will have different levels of prior knowledge for learning how to teach primary science, hence, a needs analysis can provide evidence for targeting specific and collective needs of course participants. Further research is required for articulating a theoretical rationale for targeting particular cohorts in primary science education.