Disclaimer: I graduated in CS from one of these "elite" colleges. I also took the JEE in 2013 when it underwent significant changes.
Back in 2011, the government decided to revamp the educational grading system by introducing "Continuous and Comprehensive Evaluation" (CCE) for class X.
We were the first batch to go through it and every assignment/internal exam had some weightage in your final grade.
Fast forward to 2013, there was a repeated attempt to bring similar change to this system. The central government merged the AIEEE and the IIT-JEE into two sets of exams - the JEE Mains and the JEE advanced.
They also introduced weightage to your XII grade marks in the final rankings - meaning you had to do well in your boards in addition to the one-day exam.
Admittedly, this was less radical than year-round performance, but it was still significant enough to tell everyone - "Hey, you need to perform all across our evaluations, not just in one exam".
This meant that you could have gone through all the folks who took the CBSE XII exams in my class - and they would have been in the top 5% (maybe even top 1%).
Having said that, at the end of the day - apart from signalling, the main reasons to get into the IIT/NITs were infrastructure, the environment and the network.
The infrastructure was way better than a smaller, private university and your entire class is filled with the top people from your batch.
Even if we conceded that the curriculum and the faculty were not at par with the top universities in the world, the talent surely is.
The extra-curriculars and the competition within ensured that you constantly honed your skills to remain relevant - we took MIT OCW courses, participated in global hackathons etc.
TL;DR - High-school test scores were relevant when it mattered in college entrance exams. The moment the weightage was lost, the relevancy was lost.
Back in 2011, the government decided to revamp the educational grading system by introducing "Continuous and Comprehensive Evaluation" (CCE) for class X. We were the first batch to go through it and every assignment/internal exam had some weightage in your final grade. Fast forward to 2013, there was a repeated attempt to bring similar change to this system. The central government merged the AIEEE and the IIT-JEE into two sets of exams - the JEE Mains and the JEE advanced. They also introduced weightage to your XII grade marks in the final rankings - meaning you had to do well in your boards in addition to the one-day exam.
Admittedly, this was less radical than year-round performance, but it was still significant enough to tell everyone - "Hey, you need to perform all across our evaluations, not just in one exam". This meant that you could have gone through all the folks who took the CBSE XII exams in my class - and they would have been in the top 5% (maybe even top 1%).
Having said that, at the end of the day - apart from signalling, the main reasons to get into the IIT/NITs were infrastructure, the environment and the network. The infrastructure was way better than a smaller, private university and your entire class is filled with the top people from your batch.
Even if we conceded that the curriculum and the faculty were not at par with the top universities in the world, the talent surely is. The extra-curriculars and the competition within ensured that you constantly honed your skills to remain relevant - we took MIT OCW courses, participated in global hackathons etc.
TL;DR - High-school test scores were relevant when it mattered in college entrance exams. The moment the weightage was lost, the relevancy was lost.