This mixed-methods study investigates whether and to what extent positive psychology constructs (classroom enjoyment, grit, and growth mindset) and Extramural English predict primary school students’ willingness to communicate in a second language (L2 WTC) both in the classroom (a fictitious but common setting for English communication among English as an Foreign Language [EFL] students) and outside the classroom (a natural and increasingly prevalent environment for EFL communication). We collect and analyze survey data from 160 EFL primary school students in Hong Kong (ages 6–13 years old). Hierarchical regression analyses reveal that L2 WTC in the classroom is predicted by classroom enjoyment, grit, and Extramural English. A slightly different picture emerges outside of the classroom, with grit, growth mindset, and Extramural English predicting L2 WTC. Semi-structured interviews (N = 8) confirm and elaborate on the quantitative findings. Our findings suggest that through grit- and Extramural English-integrated intervention programmes, EFL teachers can improve young learners’ L2 WTC both inside and outside the classroom. Furthermore, teachers can improve young learners’ L2 WTC in the classroom by creating a positive learning environment, while also improving their L2 WTC outside of the classroom by cultivating their growth mindset system. Copyright © 2022 Informa UK Limited, trading as Taylor & Francis Group.