Co-Ed School debuted in October 2010 with the single "Too Late". Their mini album, Something That Is Cheerful and Fresh, was released on October 28, 2010. Core Contents Media announced that it would be dividing the group into two sub-units in 2011. The female members, Soomi, Chanmi, Hyoyoung and Hyewon were joined by new member Eunkyo for female sub-unit "F-ve Dolls". Following the groups debut, they had a comeback later in the year, ultimately postponing the male groups debut. On November 4, 2011 it was announced that member Kangho was leaving the group to focus on an acting career. He was replaced by Superstar K3 contestant Shin Jongkook and the sub-unit's debut was slated for an early 2012 date.
2012: Debut with "Lovey-Dovey Plus" and Line-up Changes
In late January, the sub-units name, Speed, was revealed, along with the announcement that they would release the digital single "Lovey Dovey-Plus", a "homage" track to T-ara's hit 'Lovey Dovey'. Ex-T-ara member Ryu Hwayoung and her twin sister Ryu Hyoyoung (from F-ve Dolls) were featured in the music video. Speed followed the release of the single with two weeks of promotions on music shows.
In February, Core Contents Media decided to add Park Sejoon to Speed's line-up. Core Contents Media then moved Coed Schools and its sub-units to their subsidiary label, GM Contents Media. In September, Kwanghaeng and Noori left the group, and were replaced by Yoohwan and Taeha in October. The group was later moved back to the main label, Core Contents Media, along with 5dolls and label mates Gangkiz.
The groups "official" debut was announced in late December 2012, confirming the release of single "It's Over". On January 6, two music videos were released for the song "Sad Promise" featuring Davichi's Kang Minkyung from the Digital single "Speed of Light". A dance version, and a drama version which features Park Bo-young, A Pink's Naeun, Ji Chang-wook, and Ha Seok-jin. On January 14, 2013, they released their debut album "Superior SPEED", along with two music videos for title track "It's Over. A dance version, and a drama version which is part 2 of the "Sad Promise" drama video. The song was produced by Shinsadong Tiger and Park Bo-young (who also starred in the drama version of the music video) was featured in the song. It was announced that Speed would return following their debut album promotions with a repackage album, Blow Speed. On February 20, 2013, the repackage was released, along with the music video for the title track 통증 (Pain).
2014: SPEED mini concert, Speed Circus, Repackage EP
Before their album release, in 2013 they did a showcase in Mongolia.From February 3–7, 2014, they performed at UNIQOL AX Hall to release their newest mini-album 'Speed Circus'. The group performed six songs, and had three guest-stars, Shannon with Dani of T-ara N4 sing two songs during the intermission and Hyewon of F-ve Dolls dancing with SPEED on song 'Hey Ma Lady'. The showcase aired on February 17 on SBS MTV to the public.
Released on February 18, 'Speed Circus' has a total of five tracks and revolves around a circus theme. There are several different genres blended into the album in an attempt to show off all seven member's musical talents. Leader Taewoon also took charge in most of the writing, composing, and producing of the album, and the group gave a lot of direct input in their choreography The title track of the album is titled “늘리러 간다 (Don’t Tease Me!)”, and fully encapsulates the circus concept[clarification needed]. The music video for "Don't Tease Me!" was shot at their showcase, and shows the group in several different circus-themed costumes. The climax of the song also features several impressive stunts performed by the members. One of the tracks is titled “왜 난 꼭 (Why I’m not?)” and is a hip-hop ballad. Combining the two medium-tempo ballad with strong lyrics created a song distinct from SPEED's previous tracks, showing their growth in their musical abilities. The music video was directed by Cha Eun-taek and was filmed in one continuous shot. Included in the mini-album is the track "Focus", a solo rap by Taewoon. Most of the music video was filmed in Los Angeles, and was released on February 17 as a teaser for the mini-album.e The final track in the mini-album is titled "Hey Ma Lady", and it continues the circus theme in a more upbeat and flirtarious song. In addition, the mini-album also has the voice edition of "Don't Tease Me!". From re-released their mini album, comeback the digital single and music video "Zombie Party" with themes zombie concept and Shannon as guest star in the music video. On April 3, SPEED released the music video for "Look at Me Now," the title track to their repackage album, which is a trap-influenced song with a strong drum beat and synth sound.