Policies shift their focus from increasing enrolment to quality improvement and enhancing the conceptual knowledge and investigating skills of the students. Students' achievement scores are generally considered the true reflectors of quality improvement. This study investigated the relationship between public sector students' physics achievement scores and their conceptual knowledge at secondary school level. In this quantitative research a self-developed achievement test was used to investigate the conceptual knowledge, validated by six experts and pilot tested. Reliability of the test was found 0.85 Cronbach Alpha. Four secondary schools were selected as clusters from which 135 students were selected randomly. Pearson correlation and independent sample t-test were used for data analysis. Significant positive relationship was found between the variables, academic achievement and conceptual knowledge gender-wise and locale-wise in the subject of physics. Effect size shows the moderate and large size practical significance. This study has some implications for stakeholders in education.