'Out-of-field teaching' refers to the practice of assigning teachers to teach subjects that do not match their training or education -- an international phenomenon that seems particularly prevalent in mathematics. This paper reports on a study evaluating the impact of a national professional learning program for out-of-field secondary mathematics teachers in Ireland. An online survey investigated teachers' beliefs about mathematics, mathematics teaching and mathematics learning, and changes in teaching practices. These teachers reported largely child-centred beliefs and practices consistent with the problem-solving orientation of the new mathematics curriculum, thus providing some evidence of the program's impact.