Lack of teachers to teach computer science (CS) and pedagogically sound introductory CS curricula remain a significant challenge facing secondary schools attempting to teach CS. This paper describes our efforts to design and pilot an online 6-week middle/high school course using Stanford's OpenEdX platform. The pedagogy, curriculum and assessment are guided by learning theory. The course leverages OpenEdX features for contextual discussions and multiple-choice assessments that promote student learning and provide feedback. The paper reports on experiences in using instructor dashboards to identify targets of student difficulty and to aid curriculum redesign.