5. If three were walking together, the teacher walks in the middle, the greater [student] on his right and the lesser [student] on his left.

Q1: Why this order?

TP (Tzvi Pittinsky): This is a commemoration to how Moshe taught Torah in the desert; (see BT Eruvin 54b) Aharon on his right side, and Aharon's sons on his left.

Rambam, Copyright (c) 1999 Project Genesis, Inc.