N.Y. Comp. Codes R. & Regs. tit. 10, § 66-1.4
A principal or person in charge of a school shall not permit a child to continue to attend such a school for more than 14 days unless a person in parental relation to the child has furnished the school with one of the documents specified in section 66-1.3 of this Subpart. Such 14 calendar day period may be extended to not more than 30 calendar days for an individual student who is transferring from out-of-state or from another country and can show a good faith effort to get the necessary evidence of immunization.