Teaching assistants (TAs) in higher education are expected to teach courses in their major subject area with little to no formal instruction in the principles of effective teaching methods. The demands on TAs time are high and there is a need for easy to access, flexible, high quality instruction to provide them with the tools necessary to be effective instructors at the college level. One method of meeting this need is to provide TAs with a "toolbox" of instructional theory and methods based on instructional design principles. In order to be effective, it is important for TAs to understand the interconnected nature of effective educational principles including: instructional design, motivation, learning environments, instructional technologies and assessment. The current study looks at the effects of a self-paced online instruction designed for TAs on their teaching efficacy, perceived teaching competence and satisfaction with knowledge of the delivered instructional concepts using a pre-post, self-report design. Thirteen TAs at a southwestern research university completed both pre and post measures of knowledge and perceptions. Findings indicate that self-paced online training in instructional design concepts significantly increased TAs' satisfaction with their knowledge of instructional theory and principles, design of learning environments and instructional technology. It further increased the significance and magnitude of their understanding of the interconnected nature of instructional principles and elements of the learning dynamic and led to appreciable knowledge change in key areas. These findings provide evidence of the benefits and utility of flexible, easily accessible training in instructional principles for TAs.