Legislative and educational reform through the first 20 years of this century has focused largely on the impact of the teacher and principal on student achievement (Kraft & Gilmour, 2016; Marshall, 2017). Principals’ influence upon achievement is second only to that of classroom teachers; however, principal impact is indirect and difficult to quantify (Leithwood, Louis, Anderson, & Wahlstorm, 2004). This mixed-methods study involved the analysis of secondary data and elicitation of teachers’ and principals’ perceptions in order to determine the impact of principals on student achievement. The quantitative portion of the study involved an analysis of secondary data including the composite ACT scores of Missouri high school juniors and the Network for Educator Effectiveness (NEE) teacher survey data. The qualitative portion of the study involved an analysis of the perceptions of teachers and principals. Following the analysis of two years of NEE teacher survey data and ACT composite data, the secondary data revealed there was not a significant positive correlation between teachers’ perceptions of principals’ abilities to promote effective instruction and student achievement. The qualitative data revealed four themes regarding the promotion of effective instruction within an observation system: frequency and duration of observations needed for professional growth, qualities of instructional leaders desired in principals, feedback on instructional practices, and barriers to improved instruction. Central to nearly all modern evaluation and observation models is the theory that when instructional practices are improved, student achievement will be improved as well (Golden, 2019; Missouri Department of Elementary and Secondary Education, n.d.).