<p>The tendency in mathematics education research or professional learning has been to view elementary school teachers through a deficit lens regarding knowledge of mathematics for teaching. But practicing teachers could have valuable practical knowledge to build on as adult learners. This discussion paper provides an example of elementary teachers who were able to transform their teaching by taking control of their professional learning process and activities with the support of a mathematics teacher educator as an <i>expert friend</i>. It considers their behaviour as adult learners to develop useful knowledge for teaching mathematics. The goal is to highlight a self-directed learning perspective to their professional learning and their perspective of useful knowledge for teaching mathematics that offer insights to support meaningful change to mathematics education.&#xa0;</p>