He is a researcher and lecturer at the University of Athens and he teaches at other universities abroad. He holds a bachelor's and master's degree in mathematics and his doctoral and postdoctoral studies in Greece and abroad focused on mathematical cognition. His research interest focuses on the investigation of the cognitive skills involved in learning mathematics and the development of differentiated learning strategies for primary and secondary mathematics. His work has been published in international research journals and in numerous international conferences as a keynote speaker. He has written books for students and teachers regarding the teaching and learning of mathematics. His work has been translated into many languages and he has trained thousands of primary and secondary school teachers worldwide. He is coordinator and member of the Academic Advisory Committee of the European Dyslexia Association.