Traditional student evaluations of teaching do not adequately assess the essential constructivist-based practices that have been recommended for effective online instruction. There is a need for student evaluation of teaching instruments that are specifically designed to provide online instructors with valid feedback about the effectiveness of their online teaching practices. The studies described in this article were undertaken to develop and validate the Student Evaluation of Online Teaching Effectiveness (SEOTE). Items for the SEOTE were written to assess constructivist-based online teaching practices represented by Chickering and Gamson's (1987) Seven Principles of Effective Teaching. The first validation study was conducted by analyzing SEOTE responses from 498 undergraduate and graduate students enrolled in online courses. Results from an exploratory factor analysis of SEOTE responses yielded four interpretable factors: Student-faculty interaction, active learning, time on task, and cooperation among students. A second study involving 809 students enrolled in undergraduate and graduate courses was undertaken to provide further validity for the SEOTE. Results from this second validation study identified and confirmed the same hypothesized four-factor SEOTE structure identified by the first validation study. (Contains 1 figure and 3 tables.)