Washington voters have narrowly approved an initiative that clears the way for up to 40 charter schools to be opened in the state over the next five years.

Initiative 1240 has clung to a narrow lead as more ballots have been counted following Tuesday's election.

This is the fourth time the proposal has been on the ballot in Washington state, where voters rejected charter schools in 1995, 2000 and 2004.

Supporters say the charter proposal would offer new choices for struggling kids and their families. Opponents say charters have a mixed track record in other states and they would take away money from regular public schools.

Proponents of charter schools raised more than $10 million to promote the idea, including $3 million from Microsoft co-founder Bill Gates.