Raposo is best known for the songs he wrote for "Sesame Street" from its beginning in 1969 through the mid-1970s, and also for a time in the 1980s. He wrote the "Sesame Street Theme" – various versions of which have opened every episode – as well as many of its most popular songs, such as "Bein' Green", "C is for Cookie", "Sing" and "ABC-DEF-GHI". A version of "Sing" recorded by The Carpenters in 1973 reached #3 on the Billboard top singles chart. For many years, most of the music used in "Sesame Street"'s film segments was also written — and often sung — by Raposo.