Early social experiences, such as caregiver scaffolding, play a crucial but disputed role in the emergence of prosociality. A longitudinal experiment examined how explicit scaffolding--such as encouragement or praise--influences helping late in the first year, when helping emerges. Eighty-three infants (40 female, 6-9 months, 54% White, 17% Hispanic/Latinx, 16% Asian) participated in up to 10-weekly home visits in which they could help an experimenter in a novel activity. Data were collected in Santa Cruz, CA between February 2018 and August 2019. Compared to the control condition, explicit scaffolding increased helping by handing out-of-reach objects, n[superscript 2] = 0.02, and, among younger infants, by cleaning up. Helping also increased with age and visit number. Using a new paradigm, this research provides experimental evidence for how adults' scaffolding shapes the emergence of helping in infancy.