Across the country, states are adopting and implementing either Next Generation Science Standards (NGSS) or new state standards inspired by NGSS. Educators and researchers play a key role in the reform process as we design professional development (PD) and curriculum to support teachers in transitioning to NGSS. In this time of transition, close analysis of NGSS classroom enactments in elementary school can help us design better supports. Our study uses the framework of teacher adaptive expertise (TAE) to conduct a qualitative content analysis of five different fourth-grade teachers enacting the same NGSS lesson, Producing Electricity. To accomplish our analysis, we first synthesized existing literature and refine a working model of TAE in the field of elementary science education. In applying the lens of TAE to our data, we also develop a model of teacher routine expertise (TRE). We empirically illustrate three characteristics of TAE in our study: allowing student agency, adapting to student emergent understanding, and facilitating student-centered science discourse. Our study shows how different teachers use TAE and TRE moves in varying degrees when enacting the same lesson. Our results indicate that TAE moves align with NGSS shifts in the elementary science classroom while TRE moves reflect a more traditional science classroom. Our results have implications for the design of in-service teacher supports during this time of reform. [For the Grantee Submission, see ED598422.]