This is part four of a five-part series looking at how illegal immigration affects U.S. border security, the criminal, health care and education systems, as well as the economy. Watch the series this week on FOX News Channel.

Betty Maldanado's neighborhood school is Lowell Elementary in Orange County, Calif. She attended that school, as did her mother, brothers and sisters. But her daughter Alena will not, because most students who attend the school now are children of Mexican immigrants (search) who don't speak English. So she's sending Alena to private school.

"It makes it difficult, because you have the kids that aren't speaking English regularly at home, aren't speaking regularly even with their friends," Maldanado said. "They only speak Spanish which makes it very difficult for them to keep up in the classroom setting."

By law, citizens and immigrants — legal or not — can be educated in U.S. public schools.

One group of angry parents showed a video showing dozens of Mexican kids coming over the border to wait for a San Diego (search) school bus. Another video shows more students from another district taking the trolley back to the Mexican border after school. Many say the influx has led to overcrowded classrooms, drained school budgets (search) and a slowed learning process.

"There is nothing I can say that is more outrageous than to see this kind of theft, because that is what it is," said parent Al Sides.

School administrators say kids on the lower rungs of the socio-economic ladder are most disadvantaged when schools become overwhelmed by large numbers of non-English speaking students. One University of Southern California study shows that 94 percent of students in the Los Angeles Unified School District (search) learn English as a second language.

One in six students in California are children of illegal immigrants though many are born in the United States and therefore are U.S. citizens. Education for children of illegal immigrants costs Golden State taxpayers almost $8 billion a year. The state ranks 48th in student achievement; nearly 50 percent can't read at grade level, 40 percent underperform in math and 30 percent drop out. Schools that repeatedly fail state proficiency tests lose millions of dollars in state and federal aid.

The fifth and last installment of this series focuses on how many U.S. businesses are employing illegal immigrants while millions of Americans are out of jobs. Look for it on FOX News and FOX News.com.

Click on the video box above for a complete report by FOX News' William LaJeunesse.