This article focuses on the longitudinal evaluative strategies used in the development of a new teaching approach for a university course with high failure rates. The subject is compulsory for all first year engineering students at our university. The evaluation has been conducted as part of a process of developmental action research, and has focused on the cognitive and implementation theories represented in the course’s instructional approach. It has been based on qualitative focus group, interview and questionnaire analyses, and quantitative pre-experimental, predictive and quasi-experimental studies. The research has been conducted over a twenty five year period to validate the theory on which teaching has been based, to establish effects of the intervention and to identify ongoing needs for the type of instruction offered in the course. Based on improvement in both spatial ability and pass rates, the materials used in the course have been published in workbook form.