I taught school during the 1970s. After I retired 6 years ago, I substitute taught for two years averaging two days per week. It was interesting to contrast what teaching in HS was like then and 30 years later.
Probably the biggest difference I noticed was in the math classes. As a HS student I was required to take only 1 math class to graduate. I took all four years of math because I really liked it. After the first year of required math, Algebra I, the classes started to really be fun as both the teacher and the students were math nerds -- we all loved math. The teacher was at ease and we students were free of the chaffing of those who didn't like math. For three years we could delve into whatever seemed interesting!
When I returned as a sub, including 3 weeks as a short term replacement teacher, I found algebra much the same--forced on everyone. However, I was most amazed at the pre-calculus course, the course normally reserved for the real hard core math students. Now, with 4 years of math required for graduation, the class was filled with folks who really didn't care for math, making the teacher's job miserable and making life for the few math lovers painfully aware of their nerdiness.
Of 100 graduating students, if you get one or two people who go on in advanced mathematics in college, you supply the US need. What force feeding everyone 4 years of math has done is ruin the experience for teachers and math loving students alike while creating a majority of students who hate mathematics.
Finally, while I am on my soapbox, I believe there is very little need for most of the people in our society to learn mathematics beyond a year of algebra. Even me, with my job as a scientist, rarely used most of what I learned. My computer essentially did most of the work for me, just as cash registers do change nowadays.
Dump the 4 years of math requirements! Let math be studied by those who love it!