This dissertation, "The Effects of Within-class Ability Grouping on Primary Students' Academic Achievement" by Hiu-wing, Michelle, Wu, 胡曉穎, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Ability grouping has been highly debated in the educational field for years. This study aimed to test the effect of ability grouping on Hong Kong children. A between-subjects design was used to investigate whether students' achievement in English would be affected by the practice of ability grouping 102 Hong Kong primary school children studying in Primary One took part in the investigation. All participants first undertook a pre-test that determined their ability level- high, average or low. 51 Students were then grouped homogeneously (HM) according to ability level while students from another 51 students were grouped in heterogeneous (HT) ability setting. After attending two English lessons on the topic of singular/plural noun, students completed the post-test and a survey on ability grouping. It was hypothesised that ability grouping would have positive effect on average and high ability students while low ability students would benefit more from heterogeneous grouping. The not significant effect between HM and HT groups, F(1,96)=0.210, p=0.648, and between the ability levels between two groupings, F(2,96)=0.020, p=0.980, found in this study failed to support the research hypotheses. The findings tended to support the work of Oakes (1985, 1995, 2005), Oakes and Lipton (1990) and Slavin (1987). Yet, it was suggested that no conclusion on the effectiveness of grouping on student learning could be reached. Further implications and recommendations were included in this research. Subjects: English language - Study and teaching (Primary) - China - Hong Kong Ability grouping in education - China - Hong Kong Academic achievement - China - Hong Kong - Psychological aspects