Helping students meet rigorous new standards and assessments begins by training K-12 educators, many of whom have been in the classroom for decades. Professional development is taking a variety of forms: intensive workshops and summer institutes; books and online instruction; off-the-shelf curricula that come with training in how to teach them; and outreach from university-based STEM education centers. Some states, too, are introducing teacher training aligned to the new Common Core math standards, appointing local and regional teacher leaders and building comprehensive toolkits to help educators. This session will describe effective professional development programs already at work and identify the most successful strategies in states that have been earliest in moving forward with new standards.