Online education for post-secondary instruction is a rapidly expanding enterprise among public and private universities. While the quantity of courses over the past 10 years has exponentially increased, the quality of these courses has not. As universities accept the challenge of creating effective and responsive online learning programs to address student demand, real concern about the best design for these online learning opportunities has arisen. In traditional classrooms and educational activities, student interaction and teacher control are negotiated to support the intellectual development and knowledge acquisition of learners. These constructivist teaching practices have proved most effective in traditional classrooms--should this not be the same in an online classroom? To this purpose, this article describes the progressive development of a valid and reliable assessment tool, Online Constructivist Learning Environment Survey--OCLES(20) with Demographic Data, for determining the constructivist design of online teaching environments. This student self-report survey seeks to provide guidance for the development of online learning environments through collection of student perceptions of teaching strategies and practices in online classrooms. Data collection beyond the initial field test of the OCLES(20) has provided further validation and suggests recommendations for further refinement of the instrument.