There are over a dozen major samba schools (escolas de samba) in Rio de Janeiro.

G.R.E.S. Mocidade Independente de Padre Miguel is a terrific example of one of the major schools. Located in Samba City near downtown, Mocidade grew out of not a samba school, but in fact a local soccer team:

A escola originou-se de um time de futebol chamado Independente Futebol Clube, cuja camisa era verde e branca em listras verticais. As comemorações dos jogos eram feitas no Ponto Chic, bairro de Padre Miguel. Quando acabavam as partidas, os jogadores, bons de bola e excelentes na percussão, se reuniam e formavam um verdadeiro bloco carnavalesco.

Thanks to Alessandro Brandão from English Experts for the audio!

Translation: The school originated from a soccer team called the Independent Football Club, whose jersey was green and white with vertical stripes. The celebrations of the matches took place at Ponto Chic, in the Padre Miguel neighborhood. When the games ended, the players, talented on the field as well as terrific drummers, would get together to form a real carnival-style bloco (samba drumming group).

Check out this amazing video of the Mocidade school rehearsing:

Click video to play.