Does size matter? Attendance numbers at SI-sessions and how it affects learning conditions

Supplemental Instruction (SI) is today a well-known academic support model to address retention and student performance in higher education. However, in studies reporting the effect of SI, the number of attendees at SI-sessions are seldom mentioned or reflected upon.
This study investigates if there is a lower, optimal, and upper number of SI-attendees for SI-sessions with viable learning conditions. A literature review of 135 publications on studies of SI-programmes was conducted combined with a survey of 44 SI-leaders and 176 SI-attendees at Lund University in Sweden.
The literature review shows that there is no consensus regarding minimum, optimum or maximum numbers for SI-session attendance size for viable learning conditions.
In the survey, the number of attendees for optimal learning conditions was estimated to 11-12 by both leaders and attendees. These respondents also estimated that if the number of attendees is below 5 or above 16 students the learning conditions are likely to suffer. In the former case this is attributed to too little collective knowledge, too few viewpoints and a risk of the SI-leader being too prominent (less active participants). In the latter case, attendees are likely to find the conditions noisy and feel that they do not get seen, while the SI-leader may have difficulties in obtaining a good structure in the session as well as getting an overview of the different group discussions.
The results hint to the importance of reporting attendance numbers at an SI-session. Otherwise it is impossible for an outsider to determine if the conditions were favourable for small group learning and thus makes it hard to judge SI’s effectiveness.