It's a brassy move by Balls and one which is sure to aggravate his colleagues. After all, remember when Labour called Cameron "Mr 10 percent" because the Tory decision to protect health spending implied 20 percent cuts to other budgets? Well, according to the FT, Balls's impromptu request would mean 12 percent cuts for other departments - rising to 20 percent if Labour also protects health spending.
They're numbers which create all sorts of internal problems for Brown. Does he back Balls's request, and risk the anger of his Cabinet (as well as undermining deficit-reduction plans)? Or does he block Balls's request, and risk the anger of one of his dwindling band of allies (as well as losing what you suspect, to him, will be a tempting investment vs cuts attack to deploy against Tories)? It's a tricky situation - and one which has been worsened by the story going public.
In the end, it's hard not to see this as leadership positioning on Balls's part. Deep down, he must know it's unlikely that he'll get the chance to spend the 2011-2014 schools budget anyway – so this is mostly about striding the post-election landscape as The Man Who Saved Schools From Cuts (until the nasty Tories got in). A pity for him, then, that the Tories' agenda for schools is their most impressive and comprehensive policy area.
UPDATE: The Standard reports that Darling is resisting Balls's request, and that the Treasury are "perplexed" at the timing of it..