Formative assessment may assist teachers in identifying gaps in learning for individual students, thereby providing an avenue for teachers to adjust instruction accordingly. The problem addressed in this study is the insufficient achievement in literacy for English language learners. English language learners may have an even greater need for teachers to utilize formative assessment practices since the additional problem of language barriers has the potential to hinder progress further. The purpose of this mixed methods study was to determine whether formative assessment had a significant impact on the academic achievement of adult English language learners. The study aimed to investigate the impact, if any that formative assessment has on the academic achievement of adult English language learners in literacy programs in the Hudson Valley area of New York State. The research design consisted of a mixed methods study with the quantitative component consisting of a quasi-experimental, non-equivalent groups design. A two group pre and posttest design was intended to address the quantitative component to determine what extent if any, a difference in test scores existed for students receiving formative assessment compared to students who did not receive formative assessment during instruction. The qualitative component of the study aimed to investigate how teachers viewed the effectiveness of formative assessment as a tool for monitoring student learning and in what ways teachers utilized that information to inform instruction. The quantitative component revealed there was no statistically significant difference in overall academic achievement, reading comprehension, or written language expression for the treatment and control groups. The qualitative component of the current study reflected the findings of previous research in this area, demonstrating that teachers require the skills and support to effectively utilize formative assessment as a means of moving learning forward, especially for students with diverse English language levels, backgrounds and learning needs. The study also found inconsistency in teachers' perceived competency and actual implementation. Future studies in this area should include significant teacher training in formative assessment, including consistency of implementation and interpretation of student feedback as a means to adjust instruction to meet the needs of individual learners. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]