The challenging of assessing formal and informal online learning at scale includes various issues. Many universities who are now promoting "Massive Online Open Courses" (MOOC), for instance, focus on relatively informal assessment of participant competence, which is not highly "quality assured". This paper reports best practices on the use of a web videoconferencing application to quality control student assignments through online oral examination at scale. In this case study, we examine the use of a simple online conferencing technology FlashMeeting (FM) by a Brazilian University to provide "quality assurance" in the assessment of twelve online postgraduate courses in Law for 20,000 students. Our research questions investigate the benefits and recommendations of using FM in online oral exams at scale. Our qualitative and quantitative data analysis centres on 3,462 short format interviews through FM conducted for this purpose by a group of around fifty assessors from September 2008 to September 2012. The effective use of FM provided evidence with respect to high quality assurance recognised by the Institution with respect to: students' identity, their knowledge and ownership of written work. The key benefits identified from the perspective of assessors and students were: reliable examination, credible technology, authentic assessment, interactive e-Viva, low cost, scalable process and practical testing in terms of time, effort and money.