I work at a private school and will sadly tell you that the author's points are actually pretty severely understated when it comes to the incentives of schools regarding this phenomenon. Differentiation is a word that gets thrown around as some tremendous necessity for schools to implement, yet in the case of math, where one could fairly easily (compared to other subjects) confidently assess the attainment of prerequisites, gauge student progress, comfort, etc., we comically either bound students who have clearly mastered materials OR happily move them along the math curve in which the deficiencies in mastery build on each other to eventually lead to a child who truly has a strong distaste for math.
More even than pre-teaching, I would encourage any parent to very actively be involved to ensuring that their child maintains a reasonable comfort with math throughout their study, and to the extent possible, pitch in to help those gaps beyond "passing" or doing "ok" in class, but to earnestly try to see if their child is comfortable. The reality is schools will very frequently PASS your child and given them fine enough grades, but I would argue that it is oftentimes almost orthogonal to how comfortable your child genuinely feels with what they've learned.
More even than pre-teaching, I would encourage any parent to very actively be involved to ensuring that their child maintains a reasonable comfort with math throughout their study, and to the extent possible, pitch in to help those gaps beyond "passing" or doing "ok" in class, but to earnestly try to see if their child is comfortable. The reality is schools will very frequently PASS your child and given them fine enough grades, but I would argue that it is oftentimes almost orthogonal to how comfortable your child genuinely feels with what they've learned.