Biology laboratory instructors play a key role in creating an optimal environment where college students try hard and enjoy their classroom experiences. This study used achievement goal perspective theory to examine the influence of instructor behaviors on science, technology, engineering, and mathematics (STEM) students' perceptions of the motivational climate (caring, task, ego) and their adaptive (i.e., effort, enjoyment, performance self-esteem, and social self-esteem) and maladaptive (i.e., shame) experiences in the biology laboratory setting. Students (N = 563; women, 65%; men, 35%) enrolled in biology laboratory courses voluntarily completed a survey during the final week of the semester. Results of two structural equation modeling analyses across gender and racial identities made two important contributions to the STEM higher education literature: (1) when instructors engaged in effective teaching behaviors, students were more likely to perceive a caring/task-involving climate and, in turn, report adaptive motivational responses (i.e., increased effort, enjoyment, self-esteem; decreased shame); and (2) neither gender nor race moderated the measurement of the latent parameters. This research has important pedagogical implications, as teaching assistants could be trained to engage in these effective behaviors to optimize students' STEM learning experiences.