Beer 's first keyboard instructor was Franz Lauska , a pupil of Johann Georg Albrechtsberger and a favoured teacher at the Berlin court . Beer also became one of Muzio Clementi 's pupils while Clementi was in Berlin . The boy made his public debut in 1801 playing Mozart 's D minor Piano Concerto in Berlin . The Allgemeine musikalische Zeitung reported : ' The amazing keyboard playing of young Bär ( a Jewish lad of 9 ) , who carried off the difficult passages and other solo parts with aplomb , and have fine powers of rendition even more rarely found in one of his age , made the concert even more interesting ' .