(CNN) -- For years, children from Ciudad Acuna, Mexico, have attended schools across the border in Del Rio, Texas, but this week that changed for students who cannot prove residency.
The local school superintendent imposed new regulations to stem what he said is a long-standing problem for the district.
"I have seen van loads of kids with plates from Coahuila State (in Mexico) pulling in front of the school," San Felipe Del Rio School Superintendent Kelt Cooper told CNN. "Everyone knows what is going on. It's real blatant."
Cooper, who joined the district 11 months ago, previously was superintendent in the border town of Nogales, Arizona, where he had to deal with similar circumstances. There, he remembered, he once had 32 students with the same home address. When district officials checked, the property was a vacant lot.
In Del Rio, Cooper said he began to notice "there was some slackness in the protocol" dealing with proof of residency.
"Border towns are really unique," Cooper told CNN in a phone interview. "There is a lot of fluidity between the two cities. Having grown up in the border, I know this is very common."
Last week, Cooper received confirmation from authorities at the International Bridge border crossing that some 540 school-age kids were crossing the bridge in the mornings.
Cooper said the situation was "getting out of hand," and on Wednesday he dispatched district staff members to the bridge to talk to the parents accompanying their children from the Mexican side. The staff was able to identify 195 students that could be barred from the district's schools if they failed to provide proof they lived within the district.
Three of the students were Carla Gomez' children. In a phone interview, Gomez told CNN she lives in Del Rio with her sister-in-law, but she travels back and forth to Ciudad Acuna to see her husband, who was deported.
On Wednesday, Gomez was stopped by school district staff and received a letter saying that her children would be dropped from enrollments if she couldn't provide proof of residency.
To prove residency, the district requires parents or guardians to provide an official document such as a utility bill, lease or proof-of-rent payment, none of which Gomez said she can provide since everything is in her sister-in-law's name. She said her only alternative may be homeschooling her children.
Cooper said he knows some of the parents who received letters are upset, especially those with children who are U.S. citizens. But he said the issue is a matter or residency, not citizenship or immigration status.
"Citizenship is a moot point. It really comes down to whether you live here," Cooper said.
"Frequently, they (Mexicans) come with the impression that their kids are U.S. citizens, so they can go to school here," he added.
"I am not U.S. Border Patrol, Customs or INS. If you are a resident here, you get to go to school here, if you don't, you don't. This is not a matter of border enforcement."
A 1982 Texas Supreme Court ruling protects students from being discriminated upon based on immigration status, but Texas law states the student must live in a school district's area to attend a school within that district.
Cooper and his staff are trying to work out a tuition system for students who cannot prove residency. He is in talks with state agencies to calculate an appropriate tuition fee, but the school board would first have to approve the program.
"We are saying if we have room, you can pay tuition. We don't want this to be a burden on taxpayers. Some of the parents we have talked to have expressed interest in paying tuition," he said.
But as Cooper has learned this week, the tuition program has proven unsuccessful in other cities. He has spoken with three superintendents of other border school districts, all of whom have said to him they tried the tuition program but it didn't work.
"I got the impression from them it was not worth the hassle," he said.
But losing non-resident students could wind up costing the district.
Cooper estimated that in a worst-case scenario, the district could lose some $2.7 million in state funding since budgets are based on attendance. There are currently about 10,000 students in the district.