The Education Secretary, Ruth Kelly, has attempted to dismiss "myths" about reforms for England's schools.
Ruth Kelly sought to reassure critics of the proposals
But her speech to an education conference received a hostile reception from delegates.
Ms Kelly offered a "categorical assurance" that the creation of trust schools would not mean more selection.
But critics still called for clearer rules on preventing a "free-for-all" in school admissions.
Ms Kelly set out her defence of the White Paper at the North of England Education Conference.
Her speech, in a sparsely-attended conference hall, sought to reassure those sceptical about the impact of self-governing trust schools, including those Labour MPs threatening to rebel against the plans.
In particular, she sought to tackle fears about changes to admissions rules.
"Crucially, trust schools will work under exactly the same code of fair admissions as other schools do now," she said.
And speaking to journalists afterwards, Ms Kelly said there was no need for the Education Bill to include amendments to reinforce the government's position on school admissions.
The trust school model was a means of reinvigorating schools, with partnerships and collaborations, and should be seen as a "bridge to better standards... not a tunnel for schools that want to go it alone".
She repeated the urgent need to improve the educational opportunities of the most deprived - when seven out of 10 children from poorer backgrounds still failed to leave school with five good GCSEs.
As well as reiterating the principles of her policy, which she says will lead to more choice and higher standards, Ms Kelly revealed some more details of how it might work in practice.
Universities will be among the organisations involved in trust schools, and she announced the names of three expected to participate: Exeter, West of England and Portsmouth.
But delegates showed few signs of being won over.
During questions Ms Kelly faced muted heckling, with a couple of calls of "shame" and "why?".
And afterwards, many of those who had heard the speech said their concerns had not been adequately answered.
Mick Storey, education cabinet member for Nottinghamshire County Council, said the speech was "really disappointing" and failed to answer the worries of local education authorities.
The White Paper suggests a wider range of providers should be involved in setting up schools, but there were concerns over school admissions from private-sector providers.
Elaine Simpson, managing director of Serco, which provides education services for Walsall, expressed fears that the trust school model could attract schools in difficult areas wanting to alter their intake.
While saying she was not against the White Paper, she wanted more reassurance that the changes would not mean narrowing choices for the poorest families and creating "sink schools".
John Bangs, the National Union of Teachers' head of education, said that it "completely failed to allay fears that the Bill will lead to a fragmented and fractured education system".
Ruth Kelly's remarks had failed to reassure school leaders, said the Association of School and College Leaders (formerly Secondary Heads Association).
General secretary John Dunford said school leaders would support many of her aims. But if trust schools were not significantly different, why were they needed?
Shadow education secretary David Willetts said Ruth Kelly had created further confusion.
"On one hand she's issuing a prospectus for the new trust schools which we were told would be independent and self-governing.
"At the same time her speech almost boasted about how limited the real powers of these schools would be."
Liberal Democrat spokesman Edward Davey said letting every school set its own admissions policy would result in schools choosing pupils, not parents choosing schools.
"Ruth Kelly's own party doesn't support this white paper, teachers don't support it and the more parents realise the impact it will have they won't support it either," he said.