This coda article offers unified theoretical accounts of the major findings of the empirical studies in this special issue of "Optimizing Second Language Practice in the Classroom: Perspectives from Cognitive Psychology." We present a theoretical framework from cognitive psychology (desirable difficulty framework) and link it to the ideas of second language (L2) difficulty. We argue that practice condition, linguistic difficulty, and individual differences need to be taken into account for creating optimal, deliberate, and systematic L2 practice. The desirable difficulty framework may serve as a theoretical foundation to better understand the role of practice on L2 acquisition, as well as to gain insights into effective L2 teaching. Future directions for research are presented to further develop this emerging field of L2 practice.