The intent of this study was to investigate changes in students’ self-efficacy, motivation, and achievement related to Formative Assessment Lesson (FAL) implementation in the Algebra 1 classroom. The effect of FAL implementation on students was examined using an embedded experimental model. Students’ self-efficacy and motivation were measured using the Sources of Middle School Self-Efficacy (SMSSE) and Activity Feeling States (AFS) scales. Student achievement was measured using a researcher-created test built from questions intended to prepare students for the Georgia End-of-Course (EOC) Test. Qualitative data were collected from monthly teacher logs and teacher interviews conducted at the end of the school year. The data were analyzed by t-test, correlation analysis, and directed content analysis. Although no statistically significant differences were present for self-efficacy, motivation, and achievement between students who participated in FALs and those who did not, the descriptive results and qualitative results suggested that FAL implementation might affect students by targeting subcomponents of self-efficacy and motivation as well as student achievement. In addition, FAL implementation might influence teachers by challenging them to move from traditional instructional strategies to instruction focusing on students and providing more opportunities for student inquiry. Keywords: Formative Assessment Lesson, High School Mathematics, Motivation, Self-Efficacy, Student Achievement