Dylan Wiliam is a British educationalist who is now the Emeritus Professor of Educational Assessment at Institute of Education, University of London. His research focus is the professional development of teachers. His 1998 book, Inside the Black Box, which he wrote with Paul Black, was a successful polemic about formative assessment, selling over 100,000 copies. He demonstrated his ideas in a 2010 BBC documentary series, The Classroom Experiment, in which a class at Hertswood School was encouraged to participate more widely in activities such as answering questions.