Through transformational leadership (TL) principals can promote teacher professional learning communities (PLCs) and strengthen teacher collective efficacy (TCE)--both of which research has shown enhance student learning. Less well understood in the literature is how these three critical variables interact. This study aims to close this gap by investigating the causal relationship between TL, TCE, and PLC drawing on 181 surveys from eight schools in one high fluency district that systematically implemented PLCs. Through a SEM analysis, TL is shown to predict both stronger PLCs and TCE, and in turn stronger PLCs are predictive of enhanced TCE. Teasing out these relationships suggests pathways leaders can use to achieve sustained improvement in student learning.