Recent research has shown that implementation of innovative programs at the classroom level continues to be a major challenge. The purpose of this study was to examine the types of modifications made during implementation of two curriculum units in two different setting types (i.e., self-contained, pull-out) to identify areas that should be considered when developing curriculum for gifted learners served through various service delivery models. Following two cohorts of third-grade teachers implementing two language arts units, results indicate that teachers made choices to modify the curricula in detrimental ways more often than in productive ways, with pull-out classroom teachers making more negative modifications. Findings of the study suggest that modifying curriculum appears to be inevitable. To utilize research-based curriculum in educational settings, teachers should be provided knowledge about how to modify the curriculum for their setting to not detract from the intended learning goals, as well as understand the essential curricular components that should not be modified.