2.Should we attend school regularly during JEE preparation?
Yes you should,
Attending school regularly improve your foundation on basics of your academics course
which is the main requirements in competitive exams like JEE. simply avoiding school
studies will not let you go anywhere and you will got stuck at a single point only. That’s why I
personally recommend to each and every students to go through your NCERT books once
every day and solve completely the exercises of the prescribed chapters of the syllabus.
Yes , You have to attend the school regularly. NCERT books are fundamental books for JEE. So listen the classes carefully and Solve problems that are left by your teacher in the class . Go through the examples in the NCERT (school) textbook. They are very valuable for the preparation of school board exams and JEE. It will be best if you finish these things as early as possible.
When you back home then take the reference book whatever you are prefered. And solve problems from there.