In this presentation given at the BERA 2014 Conference in London we share how we have designed an exploratory learning environment (Fractions Lab) that allows students to interact with various fractions representations, add or subtract them and check their equivalence. Associated exploratory tasks challenge students to solve problems while the ‘epistemic affordances’ of Fractions Lab take advantage of their intuitive ideas but also challenge them to reflect on the feedback provided. The main objective is to challenge pre-conceived ideas of how fractions are represented and how Fractions Lab can create an environment for students to develop 'situated' abstractions about fractions. In the presentation we will identify some key design decisions (e.g. introducing explicit tools to encourage students to understand that there are underlying structures common to all representations) and discuss how they evolved from the literature and during design experiments, as well as how they impacted upon students' conceptual change. We conclude that students' interaction with Fractions Lab provokes them to think conceptually about fractions and to capitalise on their intuition, discouraging them from simply procedurally calculating an answer.