Hello,

The eligibility criteria for admission into IISER is:-

• candidate must be 2019 or 2020 passout to take an admission in 2020 session. This means that any candidate get only two attempts only. First attempt is the year he/she has passed +2 and other one is the coming year. if you passed your +2 in year 2020 then you can appear for session 2020 and 2021.
• They intake candidates through 3 channels. They are :- KVPY channel , Jee Advance channel , SCB channel.

which means that there is no longtterm students scope to be eligible for iiser. it's just two year and two attempts.

There 7 performance criteria which are described by the board and how the marks will be considered is explained stepwise. please follow the link:-

http://www.iiseradmission.in/index.php/pages/eligibility

Hope it helps!