The present study aimed to investigate the impact of language assessment literacy enhancement (LALE) on Iranian high school EFL students’ assessment as learning of writing skill. It also aimed to examine if LALE affects Iranian EFL students’ attitudes toward assessment as learning. To this end, 80 intermediate-level high-school EFL learners were selected and randomly categorized into the experimental and control groups. Both groups wrote an essay in the pre-test phase. Then, The ESL Composition Scale was used to teach the students what makes good writing and what criteria and standards they are supposed to learn to be able to write and rate the essays of their own and their peers. The control group received no instructional information on assessment rubrics. The experimental and control groups wrote another essay on a specific topic in the post-test phase. In the qualitative phase of the study, ten high school EFL students from the experimental group were interviewed regarding their attitudes toward the practice of assessment as learning of the writing skill in their English classes. The findings indicated that LALE significantly affected Iranian high school EFL students’ assessment as learning of writing skill. Moreover, students believed peer and self-assessment techniques are rarely implemented in Iranian high school EFL classes. They were also uncertain and felt uncomfortable judging, evaluating, criticizing, and rating their peers. Besides, they felt that they were not knowledgeable and capable enough to play the role of an assessor.