While one cannot dispute the figures re our maths science status, one must remember that there are more than 28,000 govt schools and many private ones, ranging from pathetic attempts to make money out of poor gullible parents, to very expensive world class ones. The point is as an average we do badly, but take your urban govt schools on their own, plus the better private schools and the figures change dramatically.  Effectively they are white English/ Afrikaans speaking schools run with effective governing bodies who hire teachers they need. The rural schools and even small town schools are generally poorly run and under resourced as well. 
There is our problem. But that there are so many poorly preforming schools which do need dramatic intervention  is true. Speak to SADTU as to why!