Multiple conceptualizations of the interrelation between assessment and learning yield three notions of assessment: assessment of learning, assessment for learning, and assessment as learning. This paper aims at uncovering roles and obstacles of assessment for learning and assessment as learning in English language classrooms in Hong Kong. Grounded upon the theory of constructivism and the notion of learner autonomy, assessment for learning and assessment as learning play vital roles in supporting students’ learning and nurturing autonomous learners in English language classrooms in Hong Kong, respectively. In particular, assessment for learning provides students with achievement targets prior to assessments, communicates assessment results with students by means of descriptive feedback, and guides teachers’ future lesson planning whilst assessment as learning equips students with abilities to set personal learning goals, monitor their own learning process, and conduct self-assessment in the course of learning. For all their desirability and perceived pedagogical efficacy, seldom are these two assessment practices operationalized in the implemented curriculum in English language classrooms, where assessment of learning prevails; such actualities can largely be attributable to local teachers’ lack of motivation to modify their existing assessment practices out of their conservative conceptualization of assessments, low metacognitive awareness as well as level of English proficiency of local students, and large class sizes in local classrooms, which are construed as local contextual factors hindering implementation of the two assessment practices. The aforementioned obstacles ought to be overcome so that the two assessment practices can be promoted and implemented in local English classrooms in distinct year levels for the sake of students’ language learning.