A major breakthrough took place when the West End Lefevre Gallery agreed to give Cooper's students a first exhibition, now as the East London Group, in November 1929. Sickert's inclusion, his only showing with the group, was an important draw. Because of wide, complimentary press coverage, the show had to be extended into December. "One of the most interesting and significant things in the London art season," said the Manchester Guardian about the first Lefevre exhibition. It covered just this one exhibition three times. The show was an enormous commercial success, too, with interest shown by Mayfair art dealers and high society (including Ramsay MacDonald, Lady Cunard, Viscount D’Abernon, and Edward Marsh, a perceptive collector). The noted critic, T W Earp, particularly praised the work of some artists and so the careers were launched of, for example, William Coldstream, Murroe FitzGerald, Archibald Hattemore, Elwin Hawthorne, Cecil Osborne, Henry Silk, Harold Steggles, Walter Steggles and Albert Turpin. By this time Cooper was an established painter, especially of music and musicians, which feature in some of the group shows. Eventually he negotiated a five-year group contract, resulting in eight annual Reid & Lefevre exhibitions through to 1936. Throughout the 1930s, a number of solo exhibitions were additionally held at Lefevre and elsewhere. Group exhibitions were also held outside London and members participated in numerous mixed shows, often alongside prominent artists.  1935 saw a touring exhibition of Canada and the US, organised through the Courtauld Institute whose founder, Samuel Courtauld, had remained an enthusiastic patron of the Group. In 1936, works by Elwin Hawthorne and Walter Steggles were included in Britain's contribution to the 1936 Venice Biennale, alongside well known and established artists. Members of the East London Group also painted stage sets and made a film documenting their activities. Phyllis Bray painted three large murals at the New People's Palace (now part of Queen Mary, University of London). John Cooper, Elwin Hawthorne, Brynhild Parker, Harold Steggles and Walter Steggles contributed to the popular range of Shell advertising posters. John Cooper played a major part in developing mosaic work through his courses at the Central School of Arts and Crafts. The last Lefevre show took place in 1936. For personal and professional reasons, John Cooper withdrew from the Group which then wound down. Lefevre believed its role in establishing the artists had been fulfilled.