Although citizenship education (CE) has been widely addressed in many countries' curricula, few studies have sufficiently explored students' learning of official CE curriculum content. Accordingly, in this study, students' responses to the CE curriculum content are investigated in a constrained social context taking an agency perspective. Drawing on qualitative data set in two high schools in China, the study revealed that the students learned the official content of the CE curriculum with agency by critiquing textbooks, spending limited time on the subject, memorizing the textbooks' contents without taking them seriously, and most importantly, deliberately determining what to be incorporated, reinterpreted, and resisted. The findings also showed that students' agentic citizenship learning resulted from the interplay of four elements: students' agentic orientations (interest and aspirations, prior political experience and knowledge, and practical evaluation); teachers' modifications of the CE content; a high-stakes testing educational system; and China's contested civic environment. The study extends the social constructivist understanding of citizenship learning and recommends reconstructing the Chinese CE curriculum, the educational system, and the civic environment to nurture agentic citizens.