In this study, instructional activities in science classrooms are examined in order to collect evidence to account for the strengths and weaknesses of Hong Kong students in scientific literacy as reported in the PISA 2000 project. The study consists of a questionnaire survey on the perceptions of classroom climate of science lessons of 17,616 Secondary 2 (S2) students and classroom observations of seven science lessons. According to students’ perceptions, science lessons were generally didactic; interactions were satisfactory but student questions and group discussions were less frequent. Class practicals were mainly demonstrations and pre-assigned investigations with detailed instruction. Classroom observations basically substantiate the findings obtained from the student survey that science lessons were didactic in nature and teacher-student interactions were mainly confined to low-order teacher questions. These problems were particularly serious when English was used as the medium of instruction. The prevalent use of highly prescriptive manuals and worksheets for practicals tended to discourage students from developing a genuine understanding of the nature and processes of scientific inquiry. These observations provide some preliminary evidence to account for the PISA finding that Hong Kong students were less successful on items that assess “recognizing questions” and “drawing conclusions.”