You used the word "rigorous", so which did you mean? The standard meaning of "rigorous class" is one that is very difficult and challenging to the students,
another definition is
extremely thorough, exhaustive, or accurate
Word meanings are context dependent, and in this case it is "rigourous" in the context of "class" and in the larger context of how well students perform in class. Thus, your provided definition in the context of your own argument implies a classroom in which students must show thorough, exhaustive, or accurate understanding of the material. IOW, nearly identical my provided definition which is most people use the phrase.
requires a great deal of work and effort on their part, and where good grades require clear demonstration that the material was mastered.
Inability or refusal of students to meet these expectations, combined with their parents complaints are primary reasons why such classes are not offered more.
And you know this how? See, I taught for nearly a decade, and I don't know this. I have heard this, but I have seen something else.
I have taught for 2 decades, my wife for 3 and most of my closest friends teach as well. I also conduct research on education in classrooms and am well versed in that literature.
Teachers that try to are forced to "dumb down" the class.
And you know THIS how?
See above.
Yes, teachers and resources matter, but your explanation of why black kids perform better in majority white schools ignores the variable that, by definition, most greatly and objectively differs between those schools and majority black schools, namely who the majority of a students classmates are.
White kids make better classmates for black kids?
Better students with fewer behavioral problems make better classmates for all kids. The data you cite shows that putting the black kids in classrooms where most other students are mostly white instead of mostly black led to significant improvements in those black kids learning.
You went to lengths to look for other variables that you don't know actually varied between the classes and completely ignored the potential impact of the variable that we know for certain differed, who the other students were. Given that race is confounded with many other student characteristics like SES, it probably is not race itself but other student characteristics related to race via other factors.
Classroom culture matters, culture is a byproduct or people, and the people that most define a classroom are the students and their parents who far outnumber the teachers and administrators.
Tell me about this culture.
IF you don't grasp that there is a culture in each classrooms that impacts student and teacher behavior, then you were not a very attentive teacher and no nothing of human behavior and social influence. Kids greatly impact each other in setting expectations for intellectual effort and disruptive behaviors, and parents heavily influence their kids in these ways, who then go to class and determine the overall tone of the classroom, which impacts the other kids.
Perhaps the observed effects of integration are that the black kids are helped by sitting next to other students more willing and able to meet the expectations of a rigorous class,
Because white kids are better suited encourage and help black kids than other black kids are?
and whose parents more likely to help push those classmates to meet those expectations.
Because black parents don't have expectations of their children?
Try a minute of rational thinking not blinded by dogma. You began the thread by acknowledging that students in white schools do better at school. Past performance impacts expectations. Kids that do better, set higher expectations for how they should do, as do their parents. Take a black kid and move him into a context where the students around him have been doing better and you'll have a social context of higher expectations and more peer examples of how to do well.