Can all human beings potentially be enlightened in this lifetime?

Does any Buddhist school or tradition make the assertion that all human beings have the capacity to be enlightened in this lifetime? Or to put it the other way are there groups of people who it just is not possible for them to become enlightened and they have to wait for a better rebirth? Do different traditions differ on this? Does any tradition make the claim that particular human beings will never be enlightened no matter what even in subsequent rebirths?