Under UIL policy, in order to participate in UIL activities, one has to establish residency within the school district one is attending or one will be ineligible for a calendar year. Also, the DEC can rule ineligible if moved for athletic purposes. This is regardless of open or closed enrollment schools.
Some are talking about moving for better opportunities. It's hard to validate that move when one moves from a school that has an A rating from TEA to a school with a D or F rating.
Unless the parents moved for work or it was a negative family situation, those kind of moves are obviously for athletic purposes and the student should be rules ineligible.
These new policies and regulations that UIL has just come out with will crack down on some of this mass transfer situation. (i.e. Duncanville girls basketball). It won't stop it completely, but having 10-15 transfers per year will cause major red flags to the UIL and they will step in DEC meetings.
Pretty sure starting next year the "brother in law" DEC meetings will cease because a UIL official will be in those meetings per the new regs.