I didn't think there were districts out there that dared to do this. How do the parents react if a child is disqualified after qualifying initially?
For the most part - not well

But there is very little they can do about it. OTOH, the few parents I've known well enough to hear their true feelings on it were actually happy after they got over being annoyed about it - our district's magnet program is heavy on loading kids up with extra work and is very rigid and structured, whereas our district also has a ton of great charter schools and some very good neighborhood schools and a gifted pull-out program where kids' intellectual and creative talents can be nurtured without weighting the kids down with hours of homework. So, ultimately, the families I know who were "kicked out" of the magnet program were much happier.
Our district has an elementary pull-out program too (96th percentile ability and achievement required), and student's don't have to requalify each year. Once kids enter middle school, there is no more "pull-out" program and honors LA/Math tracks replace the gifted program for all kids except the exceptionally gifted level (> 99th percentile). Entry into the honors program doesn't depend on IQ but on achievement test scores given to all district kids at the end of elementary. The pull-out gifted kids used to be required to requalify based on those, but parents who's kids didn't qualify were really REALLY upset and successfully collectively convinced the school district gifted program to drop that qualification for their kids so that kids who had an off day wouldn't get dropped. I expect there are kids who really wouldn't meet the qualifications no matter how many tests they'd taken simply because it's possible to wiggle-into the pull-out program if you have a teacher really pulling for your student in early elementary, and the pull-out program doesn't push kids ahead in terms of skills, it instead focuses on different types of learning experiences for enrichment, plus the achievement score to get in can be in either math or reading, doesn't have to be in both, so you could have kids who are strong in one, not the other but still auto-qualifying for both.
The magnet program continues, and there is another program in high school, all require re-testing to qualify.
polarbear