This study examined the formative assessment practices of three teachers in English as a Second Language (ESL) classrooms using a sociocultural theoretical framework. The study was conducted in a postsecondary ESL setting at a large public university in the southeastern United States. Using an embedded mixed methods design, this study employed teacher interviews and classroom observations to address the overarching question: What individual and contextual factors are present in the formative assessment practices of participant ESL teachers? The study also explored the relationship between student metacognitive judgments of learning (JOL) and performance with the purpose of informing formative assessment practice. To this end, 51 students responded to pre and post surveys on their metacognitive beliefs and judgments of learning questionnaires prior to three unit tests. Summary reports of students’ JOL were provided to teachers for their review and use. Findings showed teachers in this ESL setting engaged in a variety of formative assessment techniques; successful implementation of their techniques were influenced by their instructional style and student attributes like attendance, class participation, and students’ academic or educational experiences. Findings also indicated the central role of assessments in this context that provided ample opportunity for formative assessment. Overall, findings point to the value of using a sociocultural theoretical lens to examine the nature of factors affecting teachers’ formative assessment practice. With regard to the use of metacognitive judgments of learning in formative assessment, findings showed a mixed relationship between student JOL and performance, and there was no change in students’ metacognitive beliefs about writing over the duration of the semester. Although teachers did not use the JOL information in their instruction, they attributed inaccuracies in judgments to students’ achievement level. These findings are limited by implementation issues and sample size. Further study is needed to understand the nature of postsecondary ESL students’ JOL in authentic assessment situations and their applicability in the formative assessment process.