The teacher needs to state the facts that support the theory of evolution in a non-confrontational way. My friend is a science teacher and he has been confronted by children he feels have been told to challenge him - when given the facts the child has always backed down. They begin to understand that it isn't just a matter of faith.
Evolution is very important in science - children that don't accept that or the reasons why the evidence is so strong are highly unlikely to succeed in any area of science. Or archaeology.