Investigating the relationship between cognitive individual differences and second language learning has been central to second language acquisition research conducted in controlled laboratory conditions and in educational instructed contexts. However, not much research to date has simultaneously explored the role of multiple cognitive abilities for L2 development or task outcomes in educational environments. In the present study, 77 secondary-school EFL learners engaged in intensive digital practice of direct questions, alongside regular classroom instruction, for a period of two and a half weeks. They completed digital pretests and, at the end of the instruction and practice period, were administered digital posttests and a pen-and-paper communicative written task. Measures of the learners’ declarative memory, implicit statistical learning and working memory capacity were taken. Mixed-effect and multiple regression models revealed that a positive interaction between implicit statistical learning and working memory capacity predicted both posttest scores and task outcomes, whereas declarative memory did not significantly relate to either measure. It is suggested that the synergetic relationship between implicit statistical learning and working memory capacity may be key to the process of updating morphosyntactic representations of direct questions with positive effects for both L2 development and use.