[XProtocol]

Neither I'm an IIT student nor have experience of it's entrance exams or preparation. But I would like to share the idea I've got from asking students who are giving JEE Mains this year. They all said to join coaching, "Taking coaching helps a lot only if you know how to properly manage time. It helps you to build foundation for it. (Be sure the coaching you're going for has good student results and especially experienced teachers) You can ask any question regarding IIT as most of the teacher there have enrolled in IIT successfully and some may have even cleared RMO (Regional Maths Olympiad). But often I've seen students giving more time to coaching than school. Hence, getting poor marks in boards. It only depends on your ability of time management and time you take to catch concept" they said. I will surely say taking what you call dummy classes is worthy if you're serious about it.

Anything I want to suggest you before you start preparing? What I've come so far, a student preparing for IIT should have his basic concept clear before starting actual preparation (going for higher difficulty level). Also you shouldn't ignore your NCERT subject books, they aren't shit.

If you decide not go for dummy classes I recommend you to at least take FIITJEE AITS (All India Test Series) as you may already know FIITJEE is all over India, taking this test will tell you where do you stand nationally, as mass number of students participate.