Teacher self-assessment can be implemented both as a tool to assess teaching efficacy and to encourage teacher selfreflection. This paper investigates the accuracy of teacher self-assessment and discusses the implications for teachers and educational institutions. It expands on previous research regarding self-inflation and the Better Than Average (BTA) effect, including the work of Jonathan D. Brown (2011), whose findings support the claim that people tend to believe they are better than others, especially for characteristics and skills that are important to them. This study specifically sought to examine whether or not the self-inflation effects that Brown observed in student cases could also be observed in teachers. The tendency of self-inflation stems from a desire to feel good about oneself, as well as cognitive (Brown, 2011) and perhaps evolutionary reasons (Trivers, 2011). Self-inflation effects may have implications for Professional Development (PD), such as making teachers less receptive to adopting new or different approaches to their current teaching practices. For this reason, as well as others, it may be useful for teachers to be aware of the pervasiveness of self-inflation. The main findings of this study were previously published in the Hawaii International Conference on Education (HICE) Conference Proceedings in 2017, and this paper includes a broadened analysis of the results.