In 2014, the Principals Australia Institute (PAI) decided to develop a national system for providing professional certification to accomplished school principals, based on the AITSL Australian Professional Standard for Principals (the Standard). ACER has been assisting the PAI in the development of valid and reliable methods whereby principals can demonstrate how they meet the Standard. This work has included conceptualising the system, developing an assessment and evaluation framework for certification, and developing guidelines for three portfolio initiatives linked to the Australian Professional Standard for Principals. The portfolio initiatives were field-tested in 2015 and a group of principals was trained to assess them. The portfolio tasks were rated high on validity and, after training, assessors demonstrated high levels of reliability in assessing portfolio entries and identifying benchmarks.