The comments are worth reading. One of the authors explains the resistance they ran into:

Many educators and administrators actually didn't try to justify the discrimination. They recognized the problem and worked to change it. However, those who resisted reform often vilified both me and my business co-founder, Dr. Lee Stiff, rather than engage with the data showing qualified students were being excluded.

Those who defended the system used several different approaches. Some claimed research showed that minority and low-income students struggled in advanced math, so placing them there would actually harm them. They accused us of trying to damage these kids by suggesting they belonged in advanced courses. Many argued that students officially labeled "academically gifted" should get priority in advanced classes, even when those students had lower test scores than unlabeled high achievers. The gifted label, they insisted, revealed potential that went beyond what test scores could measure.

The strongest resistance came from the academically gifted departments in schools. In the first large district where school counselors saw our data and tried unsuccessfully to enroll top-scoring students in advanced math, they eventually asked for objective enrollment criteria. The AG department opposed this because, they said, the AG students might not meet such criteria. Much to our surprise, when we looked at the data, many of the AG students actually had low math scores but were still placed in advanced math classes.

They also suggested low-income families couldn't afford tutors, so advanced placement would set these students up for failure, despite no evidence that tutoring was necessary for success. Perhaps most troubling, multiple districts told us they needed high-achieving, self-motivated low-income students in standard classes to help manage inclusion of special education students. Since teachers had to focus on special needs students, they relied on these capable students to work independently and not require attention.

Rather than address the data, they primarily tried to discredit our research and questioned our motives for highlighting these disparities. They also changed reporting methods to make the exclusion patterns less visible, combining achievement levels and altering how information was presented to schools and the public.

People also seemed to think we were advocating to lower the bar so that minority and low-income students could enroll in advanced math.

…

My business partner was a math ed professor at NCSU and had taught most of the math teachers. They couldn't speak math word salad to us. He was also past president of National Council of Teachers of Mathematics, and very well liked by math teachers. The new principal sat there on her phone not listening. The math teachers told us she was "from this neighborhood and understood how things worked." Dr. Stiff showed them the data, tried to reason with them, then he got on his knees and said, "okay I am now begging you to let these kids stay in the top track." They just said no. They said parent pressure would be too much.

As far as the other parents, those of the low-income kids, they have no social capital. Many went to their churches for help. The Black Baptist community in Raleigh has all sorts of services to help parents advocate. We would work with them to help them advocate one kid at a time.

I’m usually reluctant to call names, but this sounds racist as hell.