This was the beginning of the filming where Grace Secular saw Lucas coming down the stairs. this was where the 180 degree rule was used as the camera travelled from grace to Lucas in order for use to achieve this camera angle.
At this point this was a stand off between Sophia and Lucas as grace had left the premises way before they even saw her.
Coincidence as they are both trying to get in the classroom.
Shot reverse shot was used at this point to show both expressions of both actors.