Such whiteboards can cost up to £3000 each
Investment in new computers and other classroom equipment can be a waste if teaching is poor, an education expert will tell a conference.
Children who are taught by the best teachers learn twice as fast as those with poor teachers, Prof Dylan Wiliam from the Institute of Education says.
Which school a child attends therefore matters much less than which teachers they have, he argues.
The government says it backs continuous professional development for teachers.
Professor Wiliam, deputy director of the Institute of Education, says that a simple method of providing continuous feedback on pupils' performance is far more effective than providing whiteboards, expensive computer equipment or even reducing class sizes.
In some contexts, money spent on these things could be money wasted, Prof Wiliam said, if teachers did not change the way they taught.
He said previous studies showed that the reduction of class sizes from 30 to 20 did not change teaching methods, and therefore the huge increase in spending it would require was not cost-effective.
He also questioned the value of the government's Building Schools for the Future programme.
"I'm in favour of cost-benefit analyses," he said.
"Let's apply to education the criteria you would apply to anything else.
"Any measures must be thought about.
"Education is expensive - about £30bn a year spent on it.
"I want children to have nice buildings and computers. But we need to look at how we can spend this money effectively."
To illustrate this idea, he says that if 60 pupils were taught in three classes of 20 pupils instead of two classes of 30, it would create 150,000 extra classes and teaching spots to fill in England.
At a cost of around £20,000 per class, the potential benefits should be weighed up against the cost.
Prof Wiliam said extra training would be needed in how to give continuous, immediate feedback.
But he will tell the Institute of Fiscal Studies conference in Cambridge the benefits could be "immense", because raising attainment is so important.
"The efforts involved will certainly be justified because raising achievement really matters, both for individuals and society.
One way of providing such continuous feedback is to use a "traffic light" system, he says.
Pupils show a green light if they have understood what has been taught, an amber one for partial understanding and a red one if they do not understand.
Or a teacher could write a sentence in French on the board, and ask children to give a thumbs up if it is written correctly, or thumbs down if they think it is not.
This way, Prof Wiliam says, a teacher can evaluate what proportion of the pupils are following the lesson, and at what speed to take the class.
The Department for Children, School and Families says that it is investing £150m in continuous professional development for teachers.
A spokesperson said Assessment for Learning (AfL) could bring "important benefits".
"We introduced AfL into our National Strategy in 2008, and want it to be rolled out everywhere.
"We believe it helps improve good practice and track pupils' progress."