Teacher effectiveness is the single most important in-school factor influencing the rates at which school children learn. Large variations in performance exist between teachers and this translates into missed learning opportunities for students. Whilst the impact of highly effective teachers on student learning is understood, the factors that account for the variance in teacher performance are less clear. In this study, novice teachers (N = 313), with six or fewer years of experience working at a tuition free public charter school, completed measures of positive affect, optimistic explanatory style, grit and satisfaction with life. At the end of the school year, teacher effectiveness was measured by student growth, principal ratings and parent satisfaction. Multiple linear regression showed that none of the traits predicted teacher performance as assessed by student growth or by parent satisfaction. Positive affect and life satisfaction were shown to positively predict principal ratings; however this finding was dismissed as likely the result of principals awarding higher scores to teachers with personality traits they found more desirable. Positive traits may not have significantly predicted teacher performance at NHA because of the charter school management organization’s adherence to systems thinking with fidelity. Teachers at NHA are asked to follow best practices and compliance is considered key to success over creativity in many circumstances. Adherence to these best practices may stamp out the individual performance variation through which the effect of positive traits would be most evident.