The aim of this qualitative case study is to investigate the fidelity to prescribed instructional practices shown by teachers in elementary classrooms. This study, conducted during the 2016-2017 Spring Term, interviewed twenty 1st to 4th grade elementary classroom teachers with reference to the fidelity measures of adherence and adaptation. NVIVO 11 software was used in data analysis. The results indicated that elementary teachers' fidelity to instructional strategies, methods, and techniques and patterns of adaptation varied according to teacher characteristics, student characteristics and context-based features. Most of the teachers stated that they used direct instruction and drama/roleplay, questioning, and play techniques and methods. Participant teachers said that they tried to use student-centred instruction in their classes, but dissonance existed between their applications and prescribed activities in the curriculum. Teachers felt hindrances to implementation included limited school facilities, lack of time, class sizes, inconsistency between their views on facilitating learning and the curriculum, and disapprobation of some prescribed activities. These reactions of teachers were sometimes based on disagreement with the prescribed curriculum rather than a misconception. This research aims to improve understanding of which instructional practices elementary teachers choose, and raise new questions about how and why teachers make changes to their practices.