PISA (Programme for International Student Assessment) is a worldwide study by the OECD intended to evaluate educational systems by measuring 15-year-old school pupils' performance in maths, science and reading. This week, David interviews Lucy Crehan, qualified teacher, author and educational consultant. Her book Cleverlands (2016) combines educational research with an exploration of the world's top performing education systems, for which she travelled to help out in schools and live with teachers in Finland, Canada, Singapore, Japan, New Zealand and Shanghai. She has worked with governments in England, Brunei and Myanmar, and spoken about her work at conferences in nine countries across four continents. She spent a year working as part of a team advising foreign governments on education reform at Education Development Trust, and now works as an independent consultant and author.