Designing and evaluating teacher development programs for graduate teaching assistants (GTAs) who teach in the laboratory is a prominent feature of chemistry education research. However, few studies have investigated the impact of a GTA teacher development program on the verbal interactions between participating GTAs and students in the undergraduate laboratory. Further, little research has been devoted to the development of an instructional model designed specifically for GTAs. This research set out to develop an instructional model to underpin a GTA teacher development program and to evaluate its impact on the cognitive and psychomotor verbal interactions between GTAs and students in the laboratory. Seven GTAs participated in the Teaching as a Chemistry Laboratory Graduate Teaching Assistant (TCL-GTA) program that featured the development and implementation of the Meaningful Learning in the Laboratory (MLL) instructional model seeking to nurture undergraduate students' cognitive, psychomotor, and affective domains of learning. The verbal interactions between each GTA and the students they interacted with were audio recorded for the entire duration of general chemistry laboratory sessions that took place before, during, and after the TCL-GTA program. The purpose of this article is to explore the influence of the TCL-GTA program on the cognitive and psychomotor verbal interactions between GTAs and undergraduate students during general chemistry laboratory sessions.