The high school, middle school and two elementary schools serving 1,150 students were closed in anticipation of the walkout by members of the Oregon Education Association.
The chairman of the school board resigned in frustration.
"I've walked a lot of bloody battlefields in my life," former school board chairman Dick Handbury said Tuesday. "And I don't want to walk in this one because I don't think there are going to be any survivors. This is going to be nasty.
"I think it's gotten to the point where maybe the only solution is to get some new blood and maybe some different ideas."
Paul Kyllo, crisis coordinator for the union, said more than 90 percent of the district's 61 teachers voted Tuesday to reject the board's latest proposal, calling it "too little, too late."
"This is the worst day of my life," said Joe Burns, a high school English teacher and union spokesman. "I don't blame (Handbury) one bit. I wish I could join him. But this is a crisis, and we've got to find a solution. And that's the sticking point. We're not finding it."
The sides have been bargaining for a year. The sticking points are teacher pay and control over cutting school days in case of a financial crisis.
In its latest offer, the board could unilaterally cut up to six days each year, but would be required to notify teachers at least 30 days in advance.
Teachers have proposed alternatives that would commit the board to restoring lost days later - if the revenue picture improves.
At the end of the last contract, teacher pay ranged from $29,008 to $52,494.
Teachers in Sandy went on strike in October, staying out 16 class days before agreeing to a contract with raises between 2.3 and 2.6 percent and settling health care issues.
(Copyright 2006 by The Associated Press. All Rights Reserved.)