The lower-division CS curriculum at the University of California, Berkeley includes a version of CS 2 that is intended to introduce students to Java as well as data structures and programming methodology. Some students in the course already have Java experience. In one course offering, students without previous Java experience received final grades that were 0.27 standard deviations below their peers who already had some Java experience (d=0.27, p<0.05). In a subsequent offering, the instructor adopted course policies and teaching strategies that made student collaboration more frequent in hopes that students without Java experience could learn from their peers with Java experience. In this highly-collaborative offering, there were no statistically significant differences in average final grades between students with and without Java experience (d=0.12, p<0.1). A smaller percentage of students dropped the highly-collaborative offering than the less-collaborative offering. This decrease in attrition was most notable for female students, from 37 percent to 5 percent.