This study aimed at discussing the benefits of portfolio assessment in assessing students' writing skills. The study explores the use of authentic assessment in the classroom. Eleven primary school children from Year 4 in a rural school in Sabah participated in this study. Data were collected by observing them during the English Language lessons and at the end of the series of observations, an interview session was conducted with each of them for triangulation. Through the observation, the children can be categorized into 4 groups of improvement, which are "emerging", "beginning", "developing" and "expanding" using the coding from British Columbia (1999). The results of this study revealed that using portfolio to assess young learners' writing skills is beneficial and effective in helping them to write in the English language classroom. The value of this study is to suggest the use of a more authentic classroom assessment, particularly in English language teaching and learning.