This report presents one solution to an online blended learning approach for Australian primary schools. It captures the innovative efforts of a team at Principals Australia Institute (PAI) to optimise whole-staff professional learning for schools implementing the KidsMatter Australian Primary Schools Mental Health Initiative (KidsMatter Primary) through an online learning platform. The journey of the KidsMatter Primary Portal, from scoping to rollout, is discussed. It consolidates years of work in the development of a nationally scalable professional learning environment for schools, from theory to practice. Accordingly, this report showcases the innovative development, trial and national evaluation of Australia’s first online blended learning platform for whole-school mental health promotion, prevention and early intervention.