Welcome to the marking revolution
Much more time, both to carry out assessments and to work out how to adjust their teaching accordingly.
Professor Black said: "You need to arrange for teachers to reflect regularly with one another on their practice, and to exchange examples of their work. This includes observing what goes on in colleagues' classrooms, such as how many pupils speak in lessons, and what they say. It all takes time."
He backed a suggestion by his research partner Professor Dylan Wiliam, of London's Institute of Education, that government resources would be better spent giving teachers more time for this of work than with cutting class sizes.
The Primary National Strategy materials are being supported with three days' professional development for heads. The scheme also encourages teachers to work together to develop their lessons. But heads must decide for themselves how to allow them the time for this.
The second pitfall, according to experts, is the marginalisation of assessment in class during the past 15 years, as steadily increasing weight has been placed on "high stakes" test results.
The Cambridge University-based Primary Review has concluded that assessment for learning is "limited by the attention that teachers feel needs to be given to ensuring that national test results are optimised".
Steve Anwyll, of the Qualifications and Curriculum Authority's curriculum division, recently confirmed this in a speech to the Association for the Study of Primary Education's annual conference. Mr Anwyll, a former head of the national literacy strategy, said: "We know from surveys of primary schools that many of them spend long periods of teaching time in test preparation. Many people would say that what that public bit of assessment (the test) does is to have a negative effect on what happens in the classroom."
The new Primary National Strategy material cites the work of Professor Black and his colleagues, and makes much of the value of teachers collaborating with their peers to develop their assessment practice.
Louise Johns-Shepherd, a senior adviser for progression with the Primary National Strategy, said the idea was not to impose any model on schools, but to give them the chance to opt to prioritise assessment for learning.
Whether assessment for learning truly takes off will be determined, Professor Black suspects, by teachers being able to commit to it the energy and attention it needs.
He said that another worry was that teachers could feel they were simply following orders in implementing another initiative. This, he said, was a mistake that lay behind an attempt to launch assessment for learning in secondaries in 2001.
Professor Black said: "The key thing to grasp is that it's not something that you can tell teachers to do. You have to live it for yourself."