To be most effective, formative assessment should be integrated by teachers into their everyday pedagogy. However, research has shown that such integration requires a significant commitment by teachers and administrators. In adult English as a Second Language (ESL) education, teacher and student turnover rates are high, funding is insufficient, and classroom time is limited. I proposed an assessment exercise (AE) that allowed teachers and students to experience a formative-assessment-like process, but without extensive training or integration into everyday classroom work. The AE consisted of students performing specified oral tasks, followed by self-, peer-, and teacher-assessment of the performance and the giving of feedback. In this study, two rounds of the AE were conducted on high-intermediate (HI) and low-intermediate (LI) adult ESL classes. Two approaches to self- and peer-assessment were utilized: scaffold-predetermined (SPD) and scaffold-self-derived (SSD). For the former, students were taught to use a rubric, developed by others, to evaluate their own and each other’s oral English. For the latter, students were guided to develop their own rubric. This study investigates the impact of these two approaches on students’ learning of oral English. At least two classes were considered for each proficiency level and intervention group. Observations, interviews, and questionnaires were employed to collect evidence on students’ learning. In this study, learning was defined to include students’ provision of assistance during oral task performance, their awareness of language problems, their motivation to learn English, and their improvement in oral proficiency as measured on a standardized test. Evidence gathered suggests participants in the SPD group, but not the SSD group, experienced improvements to learning as a result of their participation. Within the SPD group, both HI and LI students experienced learning gains, although the HI students appeared to benefit more. Results tend to support the introduction of this limited form of formative assessment into adult ESL classrooms as an interim step.