Which amendment led to reservation for the OBCs in institutions of higher education?

93rd Amendment

In addition to reservations, there have been a number of laws passed to end, prohibit and punish caste discrimination, specially untouchability. One of the earliest such laws was the Caste Disabilities Removal Act of 1850, which disallowed the curtailment of rights of citizens due solely to change of religion or caste. The most recent such law was the Constitution Amendment (Ninety Third Amendment) Act of 2005, which became law on 23rd January 2006. Coincidentally, both the 1850 law and the 2006 amendment related to education. The 93rd Amendment is for introducing reservation for the Other Backward Classes in institutions of higher education, while the 1850 Act was used to allow entry of Dalits to government schools.