Supplemental instruction (SI) is a widely implemented peer-led academic support program. Assessments of SI's effectiveness are often confounded by student ability, achievement, motivation and demographic characteristics, and frequently limited by available resources. We modelled the impact of SI attendance on the grades, pass rates and retention of over 4000 university students. Percentage grade increases of up to 10.4% were associated with a full semester of SI attendance, and largest for males, younger students and those who had not previously engaged with the program. Furthermore, pass rates were 10% higher for full attendees. Finally, full attendance was associated with a 3% and 9% increase in the probability of reenrolling the following year for students who had and had not previously engaged, respectively. These estimates were calculated controlling for measures of ability, achievement and motivation, plus several demographic factors. Our methods can be applied to evaluate any opt-in academic support program.

补充教学（SI）是一项广泛实施的由同伴主导的学术支持计划。对SI有效性的评估通常与学生的能力，成就，动机和人口统计学特征相混淆，并且经常受到可用资源的限制。我们模拟了SI出勤率对4000多名大学生的成绩，及格率和保留率的影响。升学率最高可达10.4％，与一整学期的SI出勤率相关，对于男性，较年轻的学生以及以前没有参与过该计划的人来说，升幅最大。此外，全场参加者的及格率提高了10％。最终，如果以前有和以前没有订过课的学生参加第二年的考试，则全勤率分别增加了3％和9％。计算这些估计值是为了控制能力，成就和动机的度量，以及几个人口统计学因素。我们的方法可用于评估任何选择加入的学术支持计划。