In science courses with large enrollments, students typically have the greatest interactions with teaching assistants (TAs) who are employed as laboratory demonstrators (Seymour, Melton, Wiese, & Pedersen-Gallegos, 2005; Percy et al., 2008) and who have a large influence over the laboratory class climate and, in turn, student retention (O'Neal, Wright, Cook, Perorazio, & Purkiss, 2007). We therefore investigated the impact of changing student-TA relations to include a sense of mentoring by redesigning TA allocations so that students worked with the same TA throughout the semester, but without changing studentto- TA ratios. Our TA training sessions also suffered from the common problem of focusing on what to teach but not how to teach (Jensen, Farrand, Redman, Varcoe, & Coleman, 2005). Therefore we incorporated advice on how to mentor and motivate students into the existing training sessions. These changes to the allocation and training of TAs were associated with improved student perceptions of their TAs' enthusiasm, knowledge, key aspects of mentoring and motivation, improvements in TAs' teaching experience, and increases in student academic performance. Conversely, these benefits were reduced for students who did not stay with their assigned TA throughout the semester. This study illustrates ways of improving student-TA relationships without increasing the number of TAs or their training time.