When Hamid walked into class on Monday, the desk next to his was empty. Sofia had sat there since the first day of school, and every morning she said hello to him in her loud, cheerful voice.

Ms. Castillo saw him staring at the desk. “Sofia’s family moved to Houston over the weekend,” she said quietly.

Hamid nodded and opened his math book, but he read the first problem three times without understanding it. At recess, he sat on the bench by himself and did not join the kickball game.

When the last bell rang, he walked slowly past Sofia’s desk. A drawing of a cat that she had taped to the corner was still there.