Despite a steady supply of equipment and continuous training, teachers' use of computers for instruction seems to be limited. Whether the problem is due to teachers' ability or usage of computers for instruction is not well understood. In order to better understand the role of ability and usage in technology integration, teachers' proficiency of technology integration was evaluated by separate ability and usage scales. Based on performance indicators from the International Society for Technology in Education (ISTE), two scales were developed that measured teachers' self-perceived ability and their frequency of usage of technology integration. The survey was administered to grade 1-9 teachers in Taiwan (n = 3729). The results showed a positive correlation between teachers' technology integration ability and usage (Pearson r = 0.56). Further examination using Structural Equation Modeling (SEM) confirmed the structure of the scales and revealed a higher correlation between the two scales after adjusting for measurement error. (Contains 2 tables, 3 figures and 1 footnote.)