I went to public schools and was in the "advanced" class for most things. We began algebra in the last quarter of 6th grade. Very basic stuff. What's a variable

I went to public schools and was in the "advanced" class for most things. We began algebra in the last quarter of 6th grade. Very basic stuff. What's a variable and how do they work. Simple equations. That kind of thing. 7th grade was nothing but algebra. The normal progression around here had (and I'm guessing still has) algebra starting in 8th. Kids handled it fine...I think. (Yes, some better than others of course.) So it surprises me that in SF, 8th grade was the year when the advanced class is just starting algebra and most not beginning until 9th. Is that the norm around the country?