The headteachers' union has warned that Tony Blair must try harder at school work in their end of term report.

At its national conference on Thursday, the National Association of Head Teachers chief David Hart rounded on the two main parties' plans for education in the next parliament.

Attacking Labour's "nanny state" tendency, the general secretary called for greater investment in schools and for more to be done to tackle the violent children of "parents from hell".

"The government's end of term report could easily read. 'tried hard, could have done better.' Pressure and support were promised in equal measure. But pressure made most of the running, support only came with a late run on the rails," he said.

In a hard hitting speech to the union's Harrogate conference, Hart warned that Labour's "script" for a second term would see an attack on school standards unless the government achieved private sector conditions - smaller class sizes and more teachers.

If the speech was tough on Labour - "An imminent general election concentrates the mind wonderfully" - Hart slammed the Tories.

"I have to say that an £8 billion tax cut looks suspiciously like no growth at all in state school resources. Their promise of self-government is theoretically attractive but more freedom to manage inadequate budgets is something of a mirage. And their total market forces system borders on social irresponsibility," he said.

Calling for smaller class sizes and greater investment in schools Hart argued that instead of talking up "miniscule" achievements the government had be held to its promises.

"Instead of just trumpeting maximum class sizes of 30 for infants, and miniscule improvements for juniors and secondary age pupils, [the government] should aim to match independent school pupil ratios of 1:11 in junior and 1:10 in senior schools."

"So we welcome the prime minister's aim to create a state education system which is as good in its facilities and investment as the independent sector. We welcome his party's commitment to spend more of the nation's GDP on education year on year on year. But if Labour are returned next Thursday make no mistake about it, we will hold him to these promises and judge his government on the outcomes next time around," he said.

Warning that the teaching profession already felt "under the cosh", Hart called on Labour to restrain its "control" instincts and trust teachers.

"It is hardly surprising that a profession, shackled by national teaching strategies, national targets, national performance tables and a national inspection system feels that it is "under the cosh"."

"Ministers and their officials can become a lethal combination when they try and control professional issues. The government's tendency so far has been to err on the side of control," Hart warned.

Saying that "it was impossible to underestimate the importance" of negotiations over teachers' workload Hart warned the government and teaching unions of the price of failure.

"It will be irresponsible if any party overplays its hand. A 35-hour week is a potentially dangerous diversion from the really key issues of class contact and management time and a boost to administrative staff in schools."

"The test for the unions is to know when they have achieved all the benefits they can legitimately expect. The test for government is to know that they have promised to deliver real improvements that significantly, not cosmetically, reduce the workload of the teaching force of this country," he said.

Key to the debate about teachers' conditions, said Hart, was the problem of violent and disruptive pupils and "the time has come to radically overhaul the exclusion system, not just to tinker with its edges".

Hart claims that in too many cases "parents have played a destructive role" and called for schools to be given more powers in banning disruptive pupils.

"Too many families are dysfunctional.Too many parents are parenting badly. Too many parents are over eager to challenge heads and their staffs. Too many parents are steeped in the blame culture and blame schools for their own inadequacies."

Speaking the day after Tony Blair promised to crack down on violence against teachers and other public sector workers, Hart said: "The simple basic fact is that there are too many 'parents from hell' that delight in making the lives of heads and their staffs as difficult as possible".