Currently teach AP and Anatomy classes in high school. Here is a rundown of who I consider to be my most intellectually talented kids. My classes are mostly made up of high achieving kids. Here's the breakdown
3 boys (2 white, one Hispanic)
7 girls (4 Hispanic, 3 white)
There is one more boy who is doing very well. He is also Hispanic. I feel his success is more a product of really high effort levels rather than innate talent. The other kids listed are also good students. There are a few other kids in my classes who I'm sure would test well on the WISC III (or whatever IQ test they administer these days), but they skate by on talent and don't really apply themselves. The kids I've listed are both highly intelligent AND highly motivated.
Our school is almost exactly split 50/50 between Hispanic and white students.
This is not to say that differences do not exist. My one low level class is almost entirely Hispanic and is 100% male. I think it's foolish to try and pin those differences entirely on native intelligence, as the OP is trying to do. There are many factors that influence academic success. Natural born intellect is only one. Others include
Home life and presence of 2 parents (as stated above)
Value placed on education by the family (I would argue that in general, white and Asian families place greater emphasis on education. My classes are far more white than brown.
Exposure to different ideas
Opportunities to travel (of my low level class, nobody has been to Yosemite National Park, despite the fact that Half Dome is visible from our school on a clear day.
Emphasis on reading at a young age.
Enrollment in tutoring programs
Nutrition
Sleep
I would argue that white and Asian parents do these things with their kids at far greater rates than Hispanic parents do. I would also argue that more affluent parents do these at a higher rate than low income parents. At our school, it mostly works out that our more affluent kids are white and more of our poorer kids are Hispanic. So, some might make the argument that brownness is the reason for poverty and low academic achievement while others make the argument that the immigrants who come to this country from south of the border are predominantly poor, have little education, have parents who don't value education, and don't have the means to provide enriching experiences that give their kids the additional tools to succeed.
This is my experience.
For another view read Hillbilly Elegy.
https://www.amazon.com/Hillbilly-Elegy-Memoir-Family-Culture/dp/0062300547
It describes the causes of generational poverty of Appalachian whites.