Author: Ray Parker and Betty Reid, The Arizona Republic; Republic reporter Jennifer Kitson contributed to this article.

Mesa and several Phoenix districts had significant enrollment declines after the holiday break in January, which officials blame on several factors, including a new state law that punishes businesses for hiring undocumented workers.

Overall, more than 1,000 students did not return to classes at Mesa Public Schools from the beginning of the school year in October to mid-year in January.

The state's new sanctions law took effect Jan. 1. Under the law, employers who knowingly hire illegal workers face the threat of losing their business licenses.

Many undocumented immigrants have reported plans to leave the state because employers, wary of the new laws, are reluctant to hire them.

"It's not entirely unexpected with this immigration law that came online January 1," Mesa school-board member David Lane said. "I have a sense unless the court intervenes, more will leave at end of the school year (in May)."

While districts often post declines midyear because of transfers, several districts showed significant enrollment declines this year.

At the Alhambra Elementary School District in west Phoenix, where enrollment numbers have been declining since spring 2007, officials will have $2 million less next school year because of the enrollment skid.

"In speaking to our community, they would share with me that undocumented families who attended our schools were concerned and they were fearful that they would be deported and their children would be left here," Alhambra Superintendent Jim Rice said.

Still, the slipping student enrollment did not generally happen in high schools.

The Phoenix Union High School District enrolled 569 more students after the winter break in January.

Phoenix Union spokesman Craig Pletenik said the employer-sanctions law worried some high-school students, but he said the teens ended up remaining in Phoenix rather than leaving the state with their families.

Dennis Dowling, director of student achievement at Tolleson Union High School District, agreed, especially for teens older than 16.

"If the families are leaving," he said, "they're finding places for the teenage kids to live."