On April 30, 2011, JYP tweeted that he had just landed in Los Angeles for recordings. The following day, he revealed that he had worked on miss A’s new song and was currently working on another song for South Korea boy group 2PM. He then uploaded a video of him at the studio with Grammy winning mixing engineer Manny Marroquin, who has worked with artist like Whitney Houston, Alicia Keys, Kanye West, and Bruno Mars. He also showed a 15-second preview of the group's new song "Goodbye Baby" which eventually became the album's lead single.
After postponing their comeback which was meant for May 2011 after the release of the single "Love Alone" in July 2011, miss A announced their comeback with their first full album called A Class which was released on July 18, 2011.
The song "Love Alone" was specially created for South Korean figure skating champion Kim Yuna's Ice Show. The group performed the song as special guests on the show as Yuna along with other figure skaters danced to the song. It was also the group's first song to be sang in English language. The song was released on May 2, 2011.
They started promoting the title song "Good Bye Baby" in July 21, 2011 on Mnet's M! Countdown and they are both promoting on KBS's Music Bank, MBC's Show! Music Core and SBS's Inkigayo. On the following week of promotions they won all awards from the shows (except Music Core which doesn't include charts on the show). They used the song "Good Bye Baby (Silver Mix)" for the comeback performance on the shows M! Countdown and Inkigayo and the song "Love Alone" on Music Bank. The group finished the promotions of the song in August 28, on SBS's Inkigayo.