This is the peer reviewed version of the following article: Ellis, R. 2015. Researching Acquisition Sequences: Idealization and De-idealization in SLA. Language Learning. 65 (1): pp. 181-209, which has been published in final form at http://doi.org/10.1111/lang.12089 This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving at http://olabout.wiley.com/WileyCDA/Section/id-828039.html