Why should they be embarrassed? It is the inability of Math teachers to instruct those who have difficulty with Mathematics. Aren’t K12 schools teaching “new m

Why should they be embarrassed? It is the inability of Math teachers to instruct those who have difficulty with Mathematics. Aren’t K12 schools teaching “new math” or whatever fad, to students and focusing on teaching to a test due to no child left behind? I wonder what studies have been done to measure how many students are math deficient in general population. Furthermore, what are approaches that could remediate such issues?