Public schools in the US state of Kansas are to be given new science standards that cast doubt on evolution.
Darwin's theory of evolution is widely accepted by scientists
The Board of Education's vote, expected for months, approved the new language criticising evolution by 6-4.
Proponents of the change argue they are trying to expose students to legitimate scientific questions about evolution.
The Kansas decision came as voters in Pennsylvania replaced all eight school board members who approved a similar policy in some of the state's schools.
Since October 2004, schools in Dover, Pennsylvania, have been obliged to read out a prepared statement on intelligent design in biology classes.
Teachers have been ordered to tell pupils that Darwin's theory of evolution is unproven, and that the universe is so complex that it may have been created by a higher power.
Last month parents in Dover sued the school board, accusing it of introducing religion and creationism into schools, in breach of the US constitutional separation of church and state.
Definition of science
Tuesday's vote in Kansas was the third time in six years that the Kansas board has rewritten standards with evolution as the central issue.
Current state standards treat evolution as well-established, a view held by national science groups.
The new standards include several specific challenges, including statements that there is a lack of evidence or natural explanation for the genetic code, and charges that fossil records are inconsistent with evolutionary theory.
It also states that says certain evolutionary explanations "are not based on direct observations... and often reflect... inferences from indirect or circumstantial evidence".
"This is a great day for education," board chairman Steve Abrams told the Reuters news agency.
Decisions about what is taught in Kansas classrooms will remain with 300 local school boards, but the new standards will be used to develop student tests measuring how well schools teach science.
Educators fear pressure will increase in some communities to teach less about evolution or more about creationism or intelligent design.
In Dover, the first US district to introduce intelligent design into schools, new school board members are thought likely to repeal the policy.
"We are all for it being discussed, but we do not want to see it in biology class," said Judy McIlvaine, a new board member.
"It is not a science."
The case against the intelligent design policy was heard in a federal court case which ended last week.
A verdict is expected early next year.