Answer
(Fatwa: 411/411=M-1429)
Tie is an emblem of Christians, and adopting the emblem of any religion is not only unlawful but also is against Islamic spirit. When tie is compulsory in your school, you should get admission in a school where such thing is not in force. If there is no such alternative school and tie is so compulsory in your school that if opposed you may be expelled out, then in such case you should wear tie only in school timings and you should never wear otherwise.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband