Paradigm contamination occurs where methods from different system development (SD) paradigms are integrated or combined. We investigate the OO and structural SD approaches and concern ourselves with the question of how paradigm contamination can be avoided when both approaches are taught at tertiary level. By comparing the techniques associated with specific SD approaches, an outline of the particular differences and commonalities that regularly cause paradigm contamination is given. Guidelines to avoid contamination traps are also provided. This is significant to instructors enabling them to make students aware of the possible contamination pitfalls as well as how to avoid them, and as a result enable them to reap the intended benefits of the chosen SD method.