California, the most populous state in the nation, removed the statewide mandate for these programs in 2014, so the timeline fits. That doesn't mean it's the predominant cause of the drop, or even a major contributing factor. But it sure doesn't help.
I've been shocked to see how little interest the public schools have in educating students who are more advanced. We live in Menlo Park, and it's like pulling teeth to get the school to allow our daughter to do advanced math. Many families are leaving the public schools because of this, and we're considering our options as well. This is a sharp contrast to my experience growing up and going to public schools in Sacramento, where there were (and still are) many good options.
But have the Gifted and Talented programs been eliminated? My children are in LAUSD, the second largest school district in the country, where we have regular Gifted and Talented meetings, including one tomorrow. No one here speaks of eliminating the programs, but I do read about it in national news sometimes.
There are zero GATE offerings here. At the district level, they said that students should be allowed to do math with the grade level that is appropriate for that student.
But at the school level, the principal has fought us every step of the way. He didn't even want to do a math assessment, which the district had promised. He literally did not want to find out what level our child is at. And the teacher has said that she does not wish for our child to learn any new math skills this year.
How do these people call themselves educators, when they aren't actually interested in educating students?
My advice would be to talk with an attorney who focuses on education and schools. These are usually special education attorneys who focus mostly on kids with disabilities but they also help gifted kids as well.
They are worth every penny. And they are the key to unlocking individualized public education.
There are ways to get an IEP for a gifted student as well, if they can qualify as twice exceptional.
"Because gifted children demonstrate greater maturity in some domains over others, they may be at greater risk for specific kinds of social-emotional difficulties if their needs are not met."
With the destruction of GATE programs and the return to local funding I imagine that there will be many lawsuits from parents like yourself asking the school districts to actually provide free appropriate public education (FAPE) for gifted kids. This may take the form of a class action Federal lawsuit. Eventually, Congress will have to act but this is going to take 5-10 years.
In the meantime you should think about private school, supplementing your child's education and see about the "twice exceptional" thing and talk to a special education attorney.
If you dive into the data, the higher performing groups are stable. Lower performing groups are falling. (E.g. non English language learners are at stable reading scores, English language learners scores keep falling).