Answer:
Those words were like magic because it helped him to gain approval from the teachers who punished them when they spoke their native Navajo language.
Step-by-step explanation:
In the mission school which Ned gained entrance to, it was forbidden for the students to speak their native language. Students caught violating this law were punished by having their mouths washed with soap. Their native names were also replaced with English names.
Ned soon learned that whenever he was called upon by the teachers, the best way to gain their approval was to answer with the words, "Yes, teacher." Answering with his native language would earn him some serious punishment.