Learning Study, in the form of action research, provides a platform for school-based teacher professional development in Hong Kong. In each Learning Study, teachers work collaboratively with researchers from the Hong Kong Institute of Education and are actively involved in the planning, teaching and assessing of the research lesson. This presentation describes one English Learning Study conducted on the topic of past tense in a Hong Kong primary school. Findings from students’ interviews, pretest and teachers’ meetings indicated that the students had difficulties in choosing and sequencing lexical and auxiliary verbs when forming yes/no questions and statements (affirmative or negative) in past tense. As such, the Object of Learning in this research lesson is to ‘build up the students’ ability to formulate yes/no questions in past tense and to provide complete answers to the questions”. The presentation outlines the whole process in conducting the Learning Study, and then examines both student learning and teacher learning in the action research.