Lines 1-3:

From the title we know this is a music "lesson" (line 1). The first line immediately alerts the reader to a shift in the action when the narrator says "Sometimes, in the middle ..." (line 1) "we exchanged places" (line 2). The reader can guess that the student and the teacher are the "we." And perhaps this is a private lesson. Oliver further evokes a shift in the reader's experience by starting the poem as if it were the middle of a larger piece. At this point, the teacher takes her place at the keyboard, and the reader can safely conclude that the poem's narrator is the student when the teacher prepares herself before playing as "She would gaze a moment at her hands / spread over the keys" (line 2).

Lines 3-6:

In concentration and in playing, the piano teacher's house vanishes from her mind, or from another perspective, she escapes...