This study examines how entrepreneurial mentoring interaction processes shape founders’ interpretations and enactment of scalability during early venture development. While prior research has established that mentoring positively influences entrepreneurial outcomes, such as self-efficacy, opportunity recognition, and strategic decision-making, it has largely treated mentoring as an input and focused on its effects rather than the interactional mechanisms through which influence unfolds. At the same time, research on scalability has predominantly emphasised structural and organisational dimensions, overlooking how founders come to adopt, or resist, a scalability-oriented mindset. Addressing this gap, the present study conceptualises mentoring as a sensegiving–sensemaking process through which meanings of scalability are constructed, negotiated, and translated into action. The study draws on a qualitative multiple-case design involving five early-stage startups participating in a structured pan-European mentoring program. The analysis is based on twenty mentoring sessions, complemented by follow-up interviews and secondary data. This dataset enables an in-depth examination of how mentoring unfolds over time as an interactional process. The findings show that mentoring introduces a conceptualised scalability evaluative regime, which emerged as a set of externally oriented criteria that redefine what counts as legitimate progress, viable growth, and credible venture development. This regime operates by shifting attention toward investor-oriented metrics, reducing dependence on founder time, enforcing representational clarity, and emphasising narrative coherence and distribution channels. However, findings from the founders’ perspective show that founders do not merely accept these criteria passively. Instead, they engage in boundary work, actively interpreting mentoring inputs through four recurring responses: acceptance, negotiation, identity-protective resistance, and deferral. These interaction dynamics give rise to three distinct scalability trajectories: (1) relabeling, where existing activities are reframed as evidence of scalability; (2) systematising, where ventures are restructured into bounded, repeatable systems; and (3) narrativising, where growth is pursued through strengthened positioning and legitimacy-building channels. The study demonstrates that scalability is not simply a structural capability but an interpretive accomplishment emerging through ongoing interaction. By shifting attention from outcomes to processes, this research contributes to entrepreneurship literature by integrating mentoring, entrepreneurial cognition, and scalability.