I wasn't kidding about the calls to CPS. I know of 2 families where CPS got involved. One of them involved a single mom who had a first grader and twin infants. She was sometimes a couple minutes late with drop-off because of juggling all the kids by herself, and once it got to about 15 tardies, CPS actually came to the school and there was a meeting.
One day my kids arrived at school literally seconds (maybe 5 seconds?) after the bell rang. The reason they were late was because someone locked the back door earlier than usual, so they had to walk around the building. The kids were sent to the office and marked tardy, and it's in the records.

I've become paranoid and if I can't get my kids out the door (with DD's ADHD and DS's organizational impairments this is often difficult), I start to panic a bit, thinking about mounting tardies. Sometimes they are marked tardy when I know I dropped them off before the bell rang. Parents aren't allowed into the school (unless they go to the office and sign in with ID), so if my kids get distracted or wander, they are marked tardy, and then I could get reported to CPS.