This discussion paper put forwards variation as a theme to structure mathematical experience and mathematics pedagogy. Patterns of variation from Marton's Theory of Variation are understood and developed as types of variation interaction that enhance mathematical understanding. An idea of a discernment unit comprising mutually supporting variation interactions is proposed and used as a building block for a mathematics pedagogy that resembles a developmental sequence from coarse idea to precise definition. Classification of plane figures is used as a pedagogical example for illustration.