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Tongue drive system (TDS) is a wireless, wearable assistive technology that enables individuals with severe motor impairments to access computers, drive wheelchairs, and control their environments using tongue motion. In this paper, we have evaluated the TDS performance as a computer input device in four tasks, commonly known as horizontal, vertical, center-out, and multidirectional rapid tapping, based on Fitts' law and ISO9241-9 Standard. Nine able-bodied subjects, who already had tongue piercing, participated in this trial over five sessions during 5 weeks, allowing us to study the TDS learning process and its current limiting factors. Subjects wore tongue rings made of titanium in the form of a barbell with a small rare-earth magnetic tracer hermetically sealed inside the upper ball. Participants performed the same tasks with a mouse (only in the first session) as a reference as well as a standard keypad for benchmarking. Six performance measures were considered, including throughput, error rate, and reaction time, all of these improved significantly from the first to the last session, and some of these plateaued over the course of the experiment. The comparison between tongue-TDS versus index-finger-keypad provides valuable insights into tongue human factors, which can lead the way in improving the usability of the TDS and similar tongue-operated assistive technologies.