This study examines and analyses the role o f the deputy principal in Irish Primary Schools in the building o f professional learning communities in the school. It focuses on what functions or tasks have been “assigned” to or negotiated with the deputy principal to improve teacher efficacy and student learning. It examines the extent to which the deputy principal and the principal are mutually supportive o f each other and other colleagues in the sustainability o f the school as a learning organisation. Twelve deputy principals from different types and size o f primary school took part in a series o f individual semi structured interviews with the researcher. The evidence from this was further corroborated by two focus groups o f principals. As the subtitle suggests a key finding is that in coping with the management o f complex change in schools today, too much responsibility cannot be left in the one ‘head’, the principal. By sharing leadership responsibility with the other ‘head’, the deputy principal this will facilitate sustainability and continuity thereby contributing to overall school effectiveness. Thus the leadership role for the deputy with the principal is similar and shared rather than separate. The overall rationale simply being that “two ‘heads’ are better than one”.