In 2009, the South Dakota Legislature increased high school graduation requirements. Previously, high schoolers could graduate with Algebra I and any two other math credits and two science credits. Now students must take the standard two years of algebra and one year of geometry plus three years of science—physical science, biology, and chemistry. Illinois increased its math and science requirements in 2005 (although only to two years of science). The American College Testing folks just issued a report saying that they don't really see much difference in Illinois students' performance on the ACT:

Examining the effects of the law on students ranking high and low academically in districts that already met the new minimum and those forced to add courses, the report found about the same statistically insignificant gain on ACT scores in science and math between both types of districts and student groups [Chris Kardish, "Does Raising High School Grad Requirements Work?" Governing, 2014.08.06].

ACT did find higher math requirements nudging college enrollment up:

Another finding: college enrollment rose faster among lower-ranking students in districts that previously required fewer math courses. The enrollment rate for low-ranking students rose 2 percent in those districts and 4 percent for higher-ranking students. But the study found no positive link between raising science standards and higher college enrollment [Kardish, 2014.08.06].

I've taught high school math and science. I'm more than happy to bust kids' brains with formulas and rigorous scientific thinking. I don't think an absence of increased test scores and only a meager boost in college enrollment is a reason to scrap tough math and science requirements. But if we're crowding out other learning opportunities for students (civics, art, world languages...) without producing demonstrable advantages, I don't mind removing legislative mandates and allowing schools to return to broader offerings for their students.