How does Kent Haruf use imagery in Where You Once Belonged: A Novel?

Imagery:

"In fact when it was their year to have him in their classrooms our teachers, by the middle of September, were already counting the days until the end of May. They had big calendars fastened to the walls with heavy Xs scratched and double-scratched through the accumulation of finished days, and one of them, Miss Ermalline Johnson, actually resigned during Christmas break rather than return for another half year."