St. Xavier's High School — About curriculum

Address:

Ramaballav road, puri, odisha, india, pin-752001

First i would like to ask are all the schools affiliated under cbse board are free to choose any other publication books other than ncert? The books cost almost a 6k and with note books extra for xaverian print. Math books are holy faith publication, english book is some other, sst books are of another different publications. All this farce upto class 9. Are they not entitled to teach from ncert prescribed books?