This chapter aims to show how insights from formal linguistic theory and empirical acquisition work can inform teaching practice in the multilingual classroom. Potential differences will arise depending on multilingual learners’ language history, particularly in the divide between true L2 and L3 learners. We show how one can use the predictions of the L3 initial stages models to predict potential areas of difficulty specifically for multilingual learners. With this knowledge, we argue, it is possible to create interventions that help learners overcome potential initial difficulties. We illustrate our line of argumentation by extending insights from published work comparing L2 and L3 acquisition, and provide an example of one such intervention that could be used to induce grammatical change (predicted) for erroneous initially transferred representations made by L3 learners.