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.