A US court decision to ban the teaching of "intelligent design" has been hailed by anti-creationism campaigners.
Charles Darwin's theory of evolution is widely accepted by scientists
A federal judge ruled in favour of 11 parents in Dover, Pennsylvania, who argued that Darwinian evolution must be taught as fact in biology lessons.
School administrators had argued that life on Earth was too complex to have evolved on its own.
Intelligent design activists criticised the ruling, saying it would marginalise beliefs based on religion.
For those fighting the policy of the Dover school board, the judicial ruling offered a boost to the separation of church and state.
About 20 US states have seen some form of challenge at local level to the pre-eminence of Darwinian evolution theory in the curriculum of publicly-funded schools since 2001.
"We have a federal judge ruling that intelligent design is in fact non-science and that it is religion," said Rob Boston of Americans United for the Separation of Church and State.
"That's going to be extremely useful as we combat intelligent design in other states."
The BBC's James Coomarasamy, in Washington, said the decision by Republican judge John Jones was a landmark ruling and represented a blow to religious conservatives.
In his ruling, Judge Jones demolished assertions by members of Dover's former school board, or administrators, that the theory of intelligent design (ID) was based around scientific rather than religious belief.
He accused them of "breathtaking inanity", of lying under oath and of trying to introduce religion into schools through the back door.
The judge said he had determined that ID was not science and "cannot uncouple itself from its creationist, and thus religious, antecedents".
In a 139-page written ruling regularly studded with criticism of the defendants' arguments, the judge said: "Our conclusion today is that it is unconstitutional to teach ID as an alternative to evolution in a public school science classroom."
Peter Briggs of the Family Research Council, a conservative group, described the ruling as a dangerous precedent.
"That's a terribly slippery slope if we're going to say in a democracy, in a free country, that people who are motivated by religion are excluded from the public script."
The ruling is not binding for schools outside Dover, but it is expected to have an impact in the wider debate over ID and the more overtly religious theory of creationism, which has long been banned from US schools.
Earlier this year, the state of Kansas passed into law the requirement that students be told that the theory of evolution was "controversial" when studying biology.
In Georgia, a federal court has been considering whether stickers questioning evolution placed on biology textbooks at one school are unconstitutional.
ID has also received backing from US President George W Bush, who has said schools should make students aware of the concept.