FREMONT -- In a deal struck days before voters decide on a school bond measure, developers of the Warm Springs/South Fremont mixed-use project have pledged to build an elementary school on land they will donate to the school district.

Land developers -- including Lennar Homes, Warm Springs Station Group and San Jose-based Valley Oak Partners -- have signed a letter of intent with the Fremont Unified School District, saying they will spend about $25 million to build a 750-student campus on five acres near the Tesla factory.

The developers also will spend $14.2 million on classrooms and other campus improvements at Walters Junior High and Kennedy High schools, district leaders have announced.

"The financial commitment ... is an unprecedented offer that no developer has made in recent memory," said school board President Lara Calvert-York. "It will provide ... educational facilities for students from this new development at no cost to the district."

During this election season, some opponents to Measure E, a $650 million bond on Tuesday's ballot, have feared that the money might be used for a new Warm Springs school, instead of improving the district's aging facilities.

Opponents also criticized developers for not spending more to offset the effects new housing will have on Fremont's crowded campuses.

Kathryn McDonald, a bond measure opponent, questions the timing of the letter of intent, which was announced less than a week before Election Day.

"The announcement of the deal might be tied to the bond measure," said McDonald, a Fremont parent. "But even if it's not, the issues with the bond remain."

The deal was announced this week because developers are at a critical juncture in building out the project, not because of the election, said Superintendent of Schools James Morris.

"We've been in discussions with developers (over the new school) for almost a year," Morris said. "The school solution sets a new standard for Fremont, and it says to the community that if we're building new housing then we have to make sure there are high-quality schools to attend in the neighborhood."

Meantime, McDonald and other opponents say the school bond -- Alameda County's largest ever -- would be wasteful because about $410 million would be spent on school improvements, with around $240 million set aside for inflation and cost overruns.

"That's nearly 60 percent set aside for overruns," McDonald said. "That's not a sensible way to manage your finances."

The bond measure would be the district's first since 2002, when voters approved a $157 million health and safety bond. The district is still paying it off. Fremont property owners each year pay nearly $31 per $100,000 of assessed value for the 12-year-old bond measure, district leaders said.

Measure E opponents also note that the Fremont school board recently approved salary hikes for teachers and other employees, costing the district $10.5 million each year in compensation.

"That money is coming out of our general fund, which we could use to repair our facilities," McDonald said. "I don't begrudge the teachers, but couldn't we have waited until the bond election first, to make sure the money is there? Making those kinds of decisions is how we got to this point in the first place."

More than 33,600 students attend 42 campuses at Fremont Unified. Enrollment has grown by 2,000 students in the past six years, and 1,500 more are expected by 2017.

In a growing district, Fremont Unified leaders have said that the plan to develop as many as 4,000 housing units near the Warm Springs/South Fremont BART station opening next year would cause a crisis in Fremont's already crowded schools.

Warm Springs Elementary, for example, already has 951 students, well above the ideal maximum, 850 students, for an elementary campus.

However, the developers' pledge to build a school there likely will ease those worries, district leaders said.

The new campus removes a key obstacle in the city's goal of "creating a regional job center" in a development that will include housing, retail and office space on 880 acres in Warm Springs, said Mayor Bill Harrison.

"I am proud of the partnership the city and school district have recently forged, and I am pleased with the commitment developers have presented to the school district," he said.

Contact Chris De Benedetti at 510-353-7011. Follow him at Twitter.com/cdebenedetti.