It's not illegal, SF public schools track it for 9th grade. They're currently discussing adding it back as an 8th grade option. This is a nonbinding resolution to signal support for it and get the school board to move their butts.
wtf for real? in my (shitty, ohio) district it's taught in 6th grade normally and starts in 4th grade for advanced students. iirc the standard 7th grade course is geometry and 8th is algebra 2