Since alternative assessment embraces highly authentic tasks consistent with classroom goals and instruction, its implementation in the language classroom is believed to promote collaboration with peers, transfer responsibility to the learners and, consequently, foster learner autonomy. This paper presents the results of a research study aiming to determine whether portfolio assessment contributes to the development of autonomy in adolescent learners. In order to collect the data, qualitative and quantative methods of research were applied. The research results reveal that the implementation of portfolio assessment failed to affect the overall level of learner autonomy. Introducing one selected pedagogical procedure does not suffice to foster learner autonomy. Teachers need to be ready to pass a portion of their authority to the learners, who, in turn, need to know how to use the new privileges judiciously.