Hillel the Elder — the Babylonian immigrant who rose to lead the Jewish people in the first century BCE — had eighty students by the end of his life. The Talmud in Sukkah 28a divides them into three classes.
Thirty of them, Hillel said, were worthy of having the Shechinah rest upon them as it had rested on Moses. Thirty more were worthy of the sun standing still for them as it had for Joshua. And twenty occupied the middle rank — great enough to carry Torah, but not in the league of the other sixty.
The greatest of them all, Hillel said, was Yonatan ben Uzziel — the author of the Aramaic Targum on the Prophets, whose mystical power, the Talmud adds, was so intense that any bird flying over his head while he studied was immediately incinerated.
The least of them was Yochanan ben Zakkai — the same Yochanan ben Zakkai who, one generation later, would be smuggled out of besieged Jerusalem in a coffin, meet the Roman general Vespasian, and win permission to found the academy at Yavneh. The man Hillel called his weakest student became the single most important rabbi of the century after the Temple's fall.
Gaster's Exempla (No. 260, 1924) preserves the ranking. The teaching underneath is simple and deep. The one Hillel thought was the least turned out to be the one Judaism could not have survived without. A teacher never really knows which student will be the hinge.