Hello sir, first of all congratulations to you and to your son as he has performed well for JEE Mains. You can check the rank of your ward based on his percentile score by using Carrers 360 rank predictor, the link of which is given below:

https://www.google.com/url?q=https://engineering.careers360.com/jee-main-rank-predictor&sa=D&source=hangouts&ust=1548220100044000&usg=AFQjCNE4NV-FhJGHaGw42SWhuxzJ6aDPnA

You can also check the probability of your son getting into any NIT's by using the same.

All the very best and i hope your son gets into some good NIT.