[Arnavion]

(I'm Indian but left India ~15 years ago, so my info may be out of date.)

It's free in government schools, what Americans would call public schools. Middle and upper class kids usually go to public schools, what Americans would call private schools, which have fees and may use non-NCERT textbooks too. I believe that for a school to be ratified it is only required that it teach at least what is mandated by the relevant education board (generally the national level one, CBSE), so it would be okay for a ratified school to use a private textbook that teaches the NCERT syllabus + periodic table + evolution.

Also college coaching classes (for IIT-JEE etc) may continue to cover these topics anyway. Even during my time they were covering topics that had been cut from the government-mandated curriculum, so it wouldn't be surprising.