New Orleans Public Schools officials estimate it will take three to five years and approximately $800 million to repair the damage caused by Hurricane Katrina.All of the system's 124 schools sustained damaged to varying degrees in the storm, said Martin McFarland, managing director for Alvarez and Marsal, the New York- based management firm in charge of the school system.About $25 million in contracts have been awarded to repair the first wave of schools with initial projects focusing on schools that can be quickly brought back into service.Construction work on 24 schools has already been put out to bid and selected. The schools with more damage will be bid on individual timetables, said McFarland.About a quarter of the schools, 32 buildings, sustained minimal damage such as blown out windows and mold growth.A lot of them were damaged only because power was off and mold started to grow due to the moisture, McFarland said.Approximately 20 Orleans Parish schools have reopened.