I taught middle school math for 3 years, and a year in the high school. I know the deficits students brought into my classroom, and I know the pains I took to try to close those gaps - usually successfully, oftentimes not.
The majority did not have a firm grasp on the times tables through 12 coming into seventh grade. It was a point of emphasis of mine to know that, as well as the squares up through 20. Some (maybe 10-15%) were still doing repeated addition even on their way out of 7th grade (i.e. instead of knowing 9x4=36, they'd write 9+9=18, 18+9=27, 27+9=36), or just falling back to their calculator. The old "you won't always have a calculator with you" canard stopped working around the time they all got cell phones, and the calculators were allowed on all standardized tests.
Fractions baffled the majority of them entirely, often even with a calculator because they struggled with Order of Operations. Number sense was definitely lacking, and it was always a point of emphasis. I'd repeatedly tell them to "Check for reality" once they got an answer... because they'd mechanically go through a series of steps and not realize that they'd made a mistake, even after the answer was so wildly off base (anecdote... 3 pairs of jeans for $51 became one pair for $0.588... divided 3 by 51 instead of 51 by 3, and didn't notice that wasn't anywhere close to making sense).
And this was in a well-off NJ suburb. I know we were ahead of a lot of other districts in the state, and certainly across the country.
Separately, I was friends with English teaches who were fighting against the current by insisting on teaching grammar... which was largely removed from the curriculum, but they were finding ways to shoehorn it in. One friend is an AP Lit teacher who was never taught grammar in school herself, and had to learn it on her own so she could properly grade papers.
There are areas where our educational system is leaps and bounds better than it was (inclusion, support for special needs, support for low income kids, etc) and areas where it's not (e.g. chasing "flavor of the month" pedagogy concepts every few years has ended up losing core competencies, focus on testing has taken away a lot of instructional time and changed the focus of that instructional time, etc).