dear student

The forms would be most probably distributed in your school and you can get the form from the regional liason officer.The application form should be signed by the Principal/ Head of the school. The candidates and the principal should adhere to the prescribed deadlines. Different states may have different deadlines. You are advised to get in touch with the liaison officer of your state for the address for the form submission.

Some schools do not enroll students but students can do so on their own. All they need is get a signature from School Principal. Please refer:http://www.ncert.nic.in/programmes/talent_exam/pdf_files/FinalLiaisonOfficerslist.pdf

You will find a liaison officer whom you can contact over email. 

NTSE Advt: http://www.ncert.nic.in/programmes/talent_exam/pdf_files/Adv.NTSE20170001.pdf

hope this helps

All the best!!!