The study explores the unaddressed washback on the English-speaking test of the Hong Kong Diploma of Secondary Education Examination (HKDSE-English Language Paper 4). The HKDSE is a university entrance exam in Hong Kong which includes a group discussion speaking test known as English Language Paper 4. To identify ongoing washback effects, including sociocultural perspectives, the study analyses ongoing student washback of test-specific and non-specific preparation and how the mediating factors affect these preparations. One-hundred and ninety-nine secondary 4th to 6th grade students provided the questionnaire data in two rounds. Results from exploratory factor analysis indicate six major types of test preparation, which are categorised as two test specific, three non-specific, and one integrated type of preparation. Mediating factors comprise five categories of learner characteristics and stakeholders in and out of school. The cluster analyses identified four students' groups intertwined with the involvement of washback and the mediating factors. A strong relationship between extrinsic factors and explicit learning and intrinsic factors and implicit learning was found. The study concludes that students' washback is affected by mediating factors aside from the test; learning method choice by students (e.g. learning from entertainment content) has a strong relationship with specific mediating factors (e.g. interest in English).