Mozart, as a child, made arrangements for keyboard and orchestra of four sonatas by now little-known composers. Then he arranged three sonata movements by Johann Christian Bach. By the time he was twenty, Mozart was able to write concerto ritornelli that gave the orchestra admirable opportunity for asserting its character in an exposition with some five or six sharply contrasted themes, before the soloist enters to elaborate on the material. Of his 27 piano concertos, the last 22 are highly appreciated.