When a school bus driver posts a lookout before backing, what is the lookout's job according to the AAMVA manual?

AAMVA CDL Manual, Section 10.7.3 (Backing), p. 10-11

If a lookout starts giving turn-by-turn directions instead of just flagging hazards, the driver may rely on someone without a full view of the hazard, or without driving training, to make maneuvering decisions. Keeping the lookout's role narrow, warn only, keeps the final driving decision with the trained driver.