On the downside Jerry Jarvis, Edexcel's managing director, who has let this genie out of its bottle (see right) worries that parents might use his data to sue schools for poor teaching, but says the information is too vital to be kept from pupils. Most schools need not worry about a flurry of writs (unless they specialise in rich pupils), though some parents may take to leaning on the head over which class their child is in.
Classroom unions suspect that heads might use data to pick off staff, ignoring other reasons for pupil underperformance. And there are fears about education itself: will data-driven teaching to the test drive out a broader acquisition of knowledge?
There are more potentially nasty genies. If pupils are, in effect, trained to pass exams, and more get top grades, will employers and universities resort to their own tests to differentiate between A* candidates? Will exam boards flog more and more monitoring tests for candidates on their courses? And what about the effect on school league tables? Yet a lot of these things happen anyway. The grapevine tells pupils and heads which teachers are the best. Students spend weeks learning not about their subject but how to structure an exam passing essay. And teaching to the test is now an art form in most schools.
What matters is that this could be a very positive development. Mr Jarvis talks of pupils identifying their own weaknesses and using the data to improve, of teachers becoming coaches, and of "truly expressive learning" as the result of freed-up teaching time. Trials have shown that grades improve, a clear benefit to hardworking pupils. Schools can compare their results with others and understand better their strengths and weaknesses. And it really could motivate pupils.
But good doesn't prevail by itself. This development deserves a proper debate at all levels of education, from teachers to the Qualifications and Curriculum Authority. The bottom line is that it must be used responsibly. The genie won't go back in the bottle, but it can be taught to behave.