Mr Schleicher said teachers needed more time and opportunities “to observe what happens in other classrooms”.
“If you look at teachers in Wales today they spend most of their time in the classroom and teachers of the future need to do lots of other things like preparing lessons with others, curriculum implementation and analysing lesson plans and professional development,” he stated.
“New teachers will have a greater level of professional autonomy and there will be more exchanging of knowledge. They need to spend more time with parents and students.”
Mr Schleicher, who is director for education and skills at the Organisation for Economic Co-operation and Development which runs PISA – the Programme for International Student Assessment – said it was “very important for a country like Wales to see if it can do better”.
He added: “It’s about lack of focus. Too many things get taught in a way that is still too shallow. High-performing countries would often teach a lot less but at a much greater depth.”
Mr Schleicher said class sizes might have to get bigger to allow teachers time off to improve their skills.
“It is very controversial but it may mean you have to accept larger classes,” he explained. “Class size is important but when you have, say, £100 do you invest it in a smaller class or opportunities for professional development?
“In the high-performing countries of Singapore and China you have 50 students in a class and highly trained teachers who teach 11 to 16 hours a week.”
Wales lagged behind the rest of the UK in the latest PISA tests taken by 3,500 15-year-olds in 2015 and published late last year.
It was the fourth consecutive set of PISA results in which Wales’s students performed worse than their peers in the rest of the UK.
The Welsh government has made it one of its top priorities to improve the nation’s performance.