Composing music, ostensibly

My sixth grade chorus teacher, Mrs. B., once passed out staff paper and asked everyone to write a treble or bass clef on the page, along with a time signature and any notes we chose, divided into measures.  She then played each student's composition on the piano.  It was interesting to me that each composition supposedly made musical sense when she played it.  Although she added chords to what each student wrote and most likely made at least a few other changes at the piano, it was nice to have the illusion that each of us could compose at least one short, compelling piece.