The purpose of this action research was to determine the impact of an interventionist conducting Tier II interventions on student achievement. The research setting was a high school English language arts classroom in Iowa where the participants included 58 ninth-grade students. In previous years, interventions were taught by the ELA teacher in the classroom; this action research dictated that an interventionist teach the Tier II intervention lesson to non-proficient students during class. Quantitative data from these participants was collected to assess the impact of an interventionist on student achievement in two reading skills: identifying the main idea and summarizing. Assessment data from the participants was then compared to assessment data from a prior year to determine the impact of using the interventionist on student achievement. The student achievement data determined there was no statistical difference in student achievement between the use of an interventionist and an ELA teacher for Tier II interventions. The researcher recommends further study be conducted, including the impact of using a long-term interventionist and how the use of an interventionist could be an asset to all students.