Marina Dubrova, an English teacher on the Russian island of Sakhalin in the Pacific, showed an uplifting YouTube video to her eighth-grade class last month in which children, in Russian and Ukrainian, sing about a "world without war.”

After she played it, a group of girls stayed behind during recess and quizzed her on her views.

"Ukraine is a separate country, a separate one,” Dubrova, 57, told them.