They have spent years working school boards, with only minimal success. Now critics of evolution are turning to a higher authority: state legislators.

In a bid to shape biology lessons, they are promoting what they call "academic freedom" bills that would encourage or require public-school teachers to cast doubt on a cornerstone of modern science.

A handful of states have considered such bills in recent years, but backers are now organizing a national movement, with high-profile help from actor Ben Stein. His new documentary, "Expelled," argues that educators suffer reprisals if they dare question evolution; in an attempt to spur action, he has held private screenings for legislators, including a recent showing in the Missouri statehouse.

The academic-freedom bills now in circulation vary in detail. Some require teachers to critique evolution. Others let educators choose their approach -- but guarantee they won't be disciplined should they decide to build a case against Darwin.