It doesn't have so much to do with the dates as it has to do with what day of the week Christmas falls on. They like to make two week breaks be two weeks of Monday through Friday off. Since Christmas is on a Tuesday this year most kids go to school until the Friday before (which is the 21st) It would be dumb to make them go to school on the 24th since that is a Monday.
Then they get two full weeks off. Since New Years is on a Tuesday, most kids do not go back until the NEXT Monday or Tuesday which would be the 7th or 8th of January.
Again, it would be dumb to make them be back at school in the middle of the week, and then get the weekend off. Monday through Friday times 2 works best for traveling and for the parents to take time off.
So, when Christmas falls LATER in the week kids are home for several days BEFORE Christmas but when it falls earlier in the week they are not.
Texas kids have the 21st (Friday) as their last day and don't return until 1/8.
You can't just look at the dates, you have to look at calendars