We study the effect of exposure to older, more experienced classroom peers resulting from the widespread use of multi-grade classes in Scottish primary schools. For identification, we exploit that a class-planning algorithm quasi-randomly assigns groups of pupils to multi-grade classes. We find that school-starters benefit from exposure to second-graders in measures of numeracy and literacy. We find no evidence that these gains are driven by smaller class sizes or more parental input. While short-lived, these benefits accrue independent of socioeconomic background, to boys and girls alike, and do not come at the expense of older peers from the preceding cohort.