This paper reports findings from two empirical studies on students’ reported use of self-regulatory writing strategies and the relationships with their writing performance in a secondary school English as a foreign language (EFL) context. Study One adopted a factorial design using exploratory and confirmatory factor analysis to validate the inferences and uses of a Self-Regulatory Writing Strategy Questionnaire; Study Two explored learner individual differences in developing self-regulatory writing strategies and the predictive effects of these strategies on students’ writing performance. Participants were two convenience samples of 669 and 239 students, who were young EFL learners in junior secondary schools in China. Results provided evidence of the construct validity of responses to the questionnaire. Students in higher grade levels reported more frequent use of self-regulatory writing strategies than those in lower grade levels, and female students reported using self-regulatory writing strategies more than male students. The six strategy factors (i.e., writing planning, goal-oriented monitoring, goal-oriented evaluation, emotional control, memorization, and metacognitive judgment) each had significant predictive effects on secondary school students’ writing performance. These findings suggest the importance of self-regulatory writing strategies to young learners’ writing performance.