Why did the girls take a different way to school?

The girls took different routes to school as to avoid unneccessary attention from the soldiers.

"I must go and speak to Ellen," Mrs. Rosen said, moving toward the door. "You girls walk a different way to school tomorrow. Promise me, Annemarie. And Ellen will promise, too."

"We will, Mrs. Rosen, but what does it matter? There are German soldiers on every corner."

"They will remember your faces," Mrs. Rosen said, turning in the doorway to the hall. "It is important to be one of the crowd, always. Be one of many. Be sure that they never have reason to remember your face."