If education policy-makers are serious about raising pupil achievement, they must focus their efforts on improving teaching, a top academic said this week.
Dylan Wiliam, professor of educational assessment at the University of London's Institute of Education, said high-quality professional development is crucial if teachers want to raise their game in the classroom.
Speaking in Newport at the first iNet Wales (International Networking for Educational Transformation) national conference, Professor Wiliam argued that achievement can only be improved by investing in teachers.
"The thing we have to get over to all our teachers is to accept the basic imperative to keep improving in practice until you retire or die," he said.
"Professional development is not something that is done so a teacher can have a bit of down time. To be effective, it must address what they do in the classroom and how they change that."
His comments came just a week after the Assembly government's draft budget revealed plans to axe continuing professional development funding for teachers from 2010.
The announcement was condemned by unions, heads and the General Teaching Council for Wales, which administered the annual pound;3 million CPD cash pot.
Professor Wiliam told delegates they must make a commitment to the continuous improvement of practice and focus on what make a difference to student outcomes.
But he also said that they must not try to be perfect and accept that mistakes are part of the learning process.
Quoting playwright Samuel Beckett, he said teachers should take as their motto a line from Worstward Ho: "Ever tried. Ever failed. No matter. Try again. Fail again. Fail better."
He also suggested their role model should be the golfer Tiger Woods, who despite being widely regarded as the best player in the world always works to refine his game further.
The day-long conference focused on school effectiveness and innovation and attracted more than 200 delegates from 84 schools.
Sylvia Paddock, iNet Wales international operations director, said the organisation is the fastest growing network worldwide - 5,500 schools across 32 countries - and attracted interest from Northern Ireland, Australia and the US.
Opening the conference, Mike Griffiths, headteacher of Cardiff High School and chairman of iNet Wales executive committee, called iNet "the perfect vehicle" to deliver the sharing of good practice.
He said: "I think iNet has the potential to transform the educational landscape in Wales. We have only just begun to scratch the surface of that potential."