Question: What school of composers was attended by the composer whose operas were considered the only German ones more important than "Die Soldaten" by Bernd Alois Zimmermann?

Context articles: Claudia Barainsky
Bernd Alois Zimmermann
Soldaten (Gurlitt)
The Soldiers (play)
Marie Angel
Alban Berg
WDR Symphony Orchestra Cologne
Die Soldaten
WDR Rundfunkchor Köln
Michael Gielen

Claudia Barainsky (born 30 September 1965) is a German operatic soprano.
 She has performed internationally, and won awards for her roles in contemporary operas such as Bernd Alois Zimmermann's "Die Soldaten" and Aribert Reimann's "Medea".
Bernd Alois Zimmermann (20 March 1918, Bliesheim, Rhine Province – 10 August 1970, Königsdorf (Frechen); full name "Bernhard Alois Zimmermann") was a West German composer.
 He is perhaps best known for his opera "Die Soldaten", which is regarded as one of the most important German operas of the 20th century, after those of Berg.
 As a result of his individual style, it is hard to label his music as avant-garde, serial or postmodern.
 His music employs a wide range of methods including the twelve-tone row and musical quotation.
Soldaten is a 1930 opera in 3 acts by Manfred Gurlitt after the play of Jakob Michael Reinhold Lenz.
 It was premiered 9 November 1930, Düsseldorf, but later overshadowed by Bernd Alois Zimmermann's setting of "Die Soldaten" (1965).
The Soldiers (German: Die Soldaten) is a 1776 comedy by Jakob Michael Reinhold Lenz written from his own experiences during his service under Friedrich Graf Kleist von Nollendorf.
 It was influential on Georg Büchner in his attempt to write the drama "Woyzeck" (left incomplete 1837), although that is set at a lower social strata.
 The play is the source of two operas "Soldaten" by Manfred Gurlitt (1930) and "Die Soldaten" by Bernd Alois Zimmermann (1965).
Marie Angel (b. Pinnaroo, South Australia, Australia, 3 June 1953) is an Australian-born opera singer.
 She sings both operas in the standard repertoire as well as contemporary operas by such composers as Mauricio Kagel, Bruno Maderna, Michael Tippett, Harrison Birtwistle, Philip Glass, Louis Andriessen, Michael Nyman, Bernd Alois Zimmermann, and John Cage.
Alban Maria Johannes Berg ( ; ] ; February 9, 1885 – December 24, 1935) was an Austrian composer of the Second Viennese School.
 His compositional style combined Romantic lyricism with twelve-tone technique.
The WDR Symphony Orchestra Cologne (WDR Sinfonieorchester Köln) is a German orchestra based in Cologne.
 The orchestra was founded in 1947 by Allied occupation authorities after World War II, as the orchestra of "Nordwestdeutscher Rundfunk" (NWDR; Northwest German Radio).
 The orchestra was named "Kölner Rundfunk-Sinfonie-Orchester" (Cologne Radio Symphony Orchestra) and from the 1990s "WDR Symphony Orchestra".
 The orchestra is particularly known for its performances of 20th-century and contemporary music.
 It has commissioned and premiered works from such composers as Luciano Berio, Hans Werner Henze, Mauricio Kagel, Krzysztof Penderecki, Karlheinz Stockhausen and Bernd Alois Zimmermann.
Die Soldaten ("The Soldiers") is a four-act opera in German by Bernd Alois Zimmermann, based on the 1776 play by Jakob Michael Reinhold Lenz.
 Written and revised in phases between 1957 and 1964, it was premiered in 1965 and dedicated to Hans Rosbaud.
 Zimmermann himself faithfully adapted the play into the libretto, the only changes to the text being repeats and small cuts.
 It is the composer's only completed opera and is considered an important work of the second half of the 20th century.
The WDR Rundfunkchor Köln (West German Radio Choir Cologne) is the choir of the German broadcaster Westdeutscher Rundfunk (WDR), based in Cologne.
 It was founded in 1947.
 The choir premiered works by contemporary composers including Arnold Schoenberg's unfinished opera "Moses und Aron" in 1954, Karlheinz Stockhausen's "Momente", Luigi Nono's "Il canto sospeso", Bernd Alois Zimmermann's "Requiem für einen jungen Dichter" and Penderecki's "St Luke Passion".
Michael Andreas Gielen (born 20 July 1927) is an Austrian conductor and composer.
 He promoted contemporary music in opera and concert, conducting premieres such as György Ligeti's "Requièm", Karlheinz Stockhausen's "Carré" and Bernd Alois Zimmermann's opera "Die Soldaten".
 He directed the Frankfurt Opera from 1977 to 1987, later called the Gielen Era, winning stage directors such as Hans Neuenfels and Ruth Berghaus, and reviving operas such as Schreker's "Die Gezeichneten" which had premiered in Frankfurt in 1918.