This is the 17871st most frequent Russian word.
успокоил
"Calmed down" or "reassured."
This usage of 'успокоил' indicates the act of reassuring or soothing someone emotionally, specifically applied to a child in distress.
Он успокоил ребёнка, который плакал.
He calmed the child who was crying.
Here, 'успокоил' reflects the teacher's endeavor to alleviate anxiety or tension among the students.
Учитель успокоил класс перед началом теста.
The teacher calmed the class before the start of the test.
In this context, 'успокоил' represents reducing fear or worry through comforting communication.