We report our research findings on Singaporean student understandings of a topic in modern physics – the photoelectric effect, discuss the possible basis of their understanding, and suggest ways to improve their understanding of this topic. This on-going research involved four junior colleges (JC). The level of the treatment of this topic in JC is similar to that of an introductory undergraduate course. The research was done using pre-test, tutorial instruction and post-test on experimental and control groups in each JC. It was found that there is a significant improvement in the experimental group over the control group for both categories of questions i.e. conceptual questions which are less familiar to our students and questions which are typical of the GCE A-Level exams.