Antioch schools' embattled superintendent has announced she will resign effective Aug. 31.

Deborah Sims made the announcement via e-mail to district employees Thursday morning, saying she wanted to give the school board adequate time to find a replacement. In the announcement, she said she is leaving to take another position but did not elaborate.

Sims declined to comment further.

On Wednesday night, the Antioch school board had been scheduled to complete a performance review of Sims with the help of an independent facilitator, but they abandoned it when she tendered her resignation, said school board President Walter Ruehlig.

"That's how the meeting started, so there was no need to move further," Ruehlig said. "Our core business is educating kids."

Sims' current contract was set to expire in 2011, and as part of the review the board would have decided whether to extend it an additional year. The district spent $6,000 to hire the facilitator.

Ruehlig said the board agreed not to comment on Sims' resignation beyond the "talking points" of the following statement:

"The board accepts the resignation of Dr. Deborah Sims as superintendent and thanks her for her service to the Antioch Unified School District. We wish her well in her future endeavors."

The Antioch school district enrolls 19,422 students and slightly fewer than 1,000 teachers. Sims was hired as superintendent in August 2006 for a base salary of $172,500. Her current base salary is $182,712.

Before coming to Antioch, Sims spent nearly her entire career with San Francisco Unified, working first as an elementary school teacher before becoming an elementary principal. She later became an assistant superintendent and associate superintendent in the district.

During Sims' tenure in Antioch, the district began a long-range reform effort to raise test scores, lower the dropout rate, and increase student engagement.

Sims oversaw the opening of two academy high schools and the development of a third, a law academy, set to open this fall at Deer Valley High School. She also led efforts to improve the district's financial standings, beefing up the rainy-day reserves and helping it obtain an AAA bond rating from Standard & Poor's.

But her tenure also had been beset by controversy.

Last fall, 86 percent of teachers cast a vote of no-confidence in her, and the district recently had been criticized for failing to promptly contact police about suspicions that an elementary school music teacher had been trying to access child pornography from a classroom computer. The district attorney's office said the delay hindered the investigation and contributed to its decision not to charge the Carmen Dragon School teacher.

Some teachers had also complained about a lack of discipline on district campuses, saying administrators were reluctant to suspend or expel disruptive students — a charge Sims denied.

Gary Hack, president of the teachers' union, said most Antioch teachers were pleased by Sims' announcement.

"It's our opinion that the superintendent's approach to leadership, her absolute lack of personal communication and her flawed decision process ... have all been matters of teacher concern basically from day one, as a union but also as individuals in the classroom," Hack said.

An Antioch mother who asked to remain anonymous had a different view. A supporter of Sims, she attributed the resignation to teacher unrest and called it "a sad day."

"It's heartbreaking that we finally have a forward-thinking superintendent and a silly thing like the teachers' union is going to get rid of the best thing we had going for us," she said.

The school board will begin its search for a new superintendent in early June.

Reach Hilary Costa at 925-779-7166 or hcosta@bayareanewsgroup.com.