In this paper, we report on the use of the swim golf (SWOLF) index as a method for assessing and predicting swimming performance. The SWOLF index is the sum of the number of arm strokes and the time needed to cover a certain distance. A reduction of the SWOLF index means improved swimming performance since a decrease of this index reflects higher technical ability and/or higher swimming speed. A total of 188 freshmen university students in Movement Sciences (59 girls, 129 boys, mean age 19 years), enrolled in an 11-lesson crawl unit, participated in this study. Front crawl was taught by a certified teacher using direct instruction (8 lessons) and peer learning (2 lessons), aiming to improve performance and skill analysis. Before and after the crawl unit, students' SWOLF index was calculated during a 50-meter sprint test. Results demonstrated a significant decrease of the SWOLF index for both female (p < 0.001, d = 0.88) and male (p < 0.001, d = 0.54) students from pretest to posttest. Based on these results, SWOLF-charts were produced visualizing expected learning outcomes based on performance level at course entry. To conclude, the SWOLF index is a promising tool for assessing swimming performance. In addition, SWOLF index percentiles can be used to predict and target individual swimming performance after well-defined educational interventions. Future work could investigate the generalizability and applicability of the SWOLF index to assess and predict swimming performance in a variety of settings.