In this paper we outline a new theoretical model of expert practice that identifies the importance of attentional skills. We report on a small-scale pilot study of the classroom practice of experienced teachers of mathematics based on this model, through which a method of articulating aspects of classroom practice has been developed. This study took place in England, where current policy in teacher education places considerable emphasis on lesson planning. Our study raises issues about the relationships between the different kinds of knowledge that we see as constituting expert practice.