Short story. When my youngest daughter was in 8th grade, she took Algebra. This was a Catholic school. She went on to take Honors courses in Math throughout HS (also Catholic). However, one of her classmates went to a public HS. When they were placing her in classes, they put her in an Algebra course. She told them that she had already taken an Algebra course. The response from the "educator" was: "The 8th grade mind cannot comprehend Algebra." So, the poor kid had to take it over again.
When I was in 8th grade, another 8th grader and I tied for the county championship in Algebra. We beat a whole slew of 9th graders.