NTA conducts the examination called AISSE which is the All India Entrance for Sainik School. The admission test is conducted for admission to the class 6 and Class9. There are no eligibility criteria except the age limit. For class 6 the age must be in the range  10-12 years, as on March 31, 2021 & for class 9 the age must be in the range 13-15 years, as on March 31, 2021.

For the AISSE syllabus visit the link below:

https://school.careers360.com/articles/sainik-school-syllabus

I hope this answer helps. All the very best for your future endeavors!