Increasing the supply of qualified teachers is a priority in many nations as a prerequisite to accomplishing UNESCO's Sustainable Development Goal 4 (SDG 4) to "ensure inclusive and equitable quality education and promote lifelong learning opportunities for all" by the year 2030. Questions remain however concerning definitions and measurement of the intended global indicators. In this article, I argue that the work of the comparative research community has the potential to inform and enrich UNESCO's SDG 4 indicators agenda concerning teachers, but this would require moving from a focus on easy to measure indicators such as teacher qualifications to more meaningful and valid indicators such as teacher qualities, and the quality of their education -- a neglected area in the SDG 4 targets. Using evidence from two cross-national studies of mathematics education I propose that engagement with comparative education research may help to re-imagine a sustainable and high-quality teaching-and-teacher education project globally.