This paper explores the relationship between development of Second Language Proficiency and the Content-Based Instructions/Teaching Materials, based on an M (Phil) research. About 350 First Year Undergraduates of seven English medium special Degree Programmes in Faculty of Management Studies, Sabaragamuwa University of Sri Lanka have been selected as the target group. A Teaching Module with three Continuous Assessments in par with CBI/TM has been developed, and the target group is taught with it in their First Year Second Semester. At the beginning of the semester and the end of the semester, a skill based Pre – test and a Post – test has been given, and the test scores have been recorded. Two groups were identified as Well Performed Group and Less Performed Group based on the Pre–test scores. The Mean Values of test scores have been compared, and the whole sample shows a -5.552 Mean Value difference indicating a positive relationship between development of Second Language Proficiency and the CBI/TM. Further, there is a remarkable progress in Less Performed Group with a -5.883 Mean Value difference signifying that newly developed CBI/TM is more effective to Less Performed Group than Well Performed Group. Also, some offshoots have been observed in the research.