That is a question the National Association for Music Education Responding standard asks students to consider. Grades 1-5 discuss a piece selected for them. Older students do the selecting. Presented here is an example for the older students, and perhaps a selection for the younger: Beethoven's Symphony No. 6, or Pastoral, which reveals Beethoven's love of nature and the sounds he heard on long walks in the country. The five movements are in public domain:  I., II., III., IV., and V. At times the music is imitative, most strikingly toward the end of  II. "Scene by the Brook," when he reproduces the calls of a nightingale (flute), a quail (oboe), and a cuckoo (clarinets). As a fun exercise for any grade, see if students can identify the three birds in the music. Recordings of their calls are also in public domain:  nightingale, quail, and cuckoo. (A composer reviewing this exercise heard one of the birds, the cuckoo, "repeating a descending major third, D# to B." Try it on piano!)