The ASKTM project (2016-2020, NSF EHR Core R&D, $1.7 million, PIs Jacobson, Bradshaw, Walkowiak) will investigate the structure of elementary teachers’ mathematical knowledge for teaching (MKT) as it is held by novice or experienced teachers, as it is learned in the context of teacher preparation and practice, and as it is used for instruction and to support student learning. The project team will develop a teacher knowledge assessment focused on fractions and decimals and subsequently examine the relationships between teacher knowledge, observed mathematics instruction, and student learning, through applications of recent advances in psychometric methods. The study aims to advance fundamental knowledge of the structure of MKT and thereby offer theoretical and pragmatic implications for the field of mathematics teacher education.