The research on using event logs and item response time to study test-taking processes is rapidly growing in the field of educational measurement. In this study, we analyzed the keystroke logs collected from 761 middle school students in the United States as they completed a persuasive writing task. Seven variables were extracted from the keystroke logs and compared with different score and gender groups. Group comparisons were also made using methodologies borrowed from sequence mining. Students' composition strategies over the course of the writing process were also investigated. The findings of this study have implications for gaining deeper understanding of observed group differences and for designing interventions to close the achievement gaps among population groups.