Parents and children filled waiting rooms the day after students were required to get immunizations, despite a monthlong extension.
Thousands of students were estimated to still be missing the new state-required shots. Parents were given an extension from the original Aug. 24 deadline to Sept. 30.
Children could be turned away from school if they did not have up-to-date shot records, but it was not immediately clear how many were not allowed to attend classes.
The line at the Dallas County Health and Human Services' Stemmons Freeway clinic was around the building as parents scrambled to get shots the day after the deadline.
State health officials extended the deadline because of a shortage of vaccine and to educate parents about the new requirements.
But Zachary Thompson, medical director of the Dallas County Health and Human Services, said parents should have been well aware of the looming deadline.
"Any child that was turned away at school today, that was the parent's responsibility," he said.
Parent Wanesha Jeffrey, whose two daughters were not allowed into school until their shot records were updated, said getting the shots was inconvenient.
"People say, 'Why did you wait until the last minute?' When you have a job and you get out at 5 p.m., there is nobody giving shots after 4 p.m.," she said.