Running from August 2012 to October 2014, the first three series were written by Jack Whitehall, who starred as Alfie Wickers, "the worst teacher ever to grace the British education system".

Despite a mixed reception from critics, the show remained "a hit with the target audience", and was adapted to a 2015 film starring the original cast.

Series 1-3 focuses on Alfred "Alfie" Wickers (Jack Whitehall) – a posh, newly graduated History teacher.

The class includes shy Joe (Ethan Lawrence), wannabe hard man Mitchell (Charlie Wernham), paraplegic rude boy Rem Dogg (Jack Binstead), sexually promiscuous Chantelle (Nikki Runeckles), camp Stephen (Layton Williams), intelligent but snooty Jing (Kae Alexander), hot-tempered Cleopatra (Weruche Opia), and school bully Frank (Jack Bence) who often bullies Alfie.

At the same time, Alfie finds himself having to cope with the antics of his eccentric, laidback headmaster, Shaquille "Simon" Fraser (Mathew Horne), and meet the expectations of a string of deputy heads: at first ruthless authoritarian Isobel Pickwell (Michelle Gomez), then the cruel yet pathetic Professor Celia "Pro Green" Green (Samantha Spiro), and then his own father, goofy and naïve Martin Wickers (Harry Enfield).

Series 4 focuses on Stephen and Mitchell, who return to Abbey Grove to teach a new cohort of Class K. The school also has a new headteacher, Bernadette Hoburn (Vicki Pepperdine), with Fraser now working in the canteen.

The new pupils are the glamorous Usma (Asha Hassan), the hustling Blessing (Francesca Amewudah-Rivers), the wannabe-rapper Inchez (Anthony J Abraham), the dim-witted Harrison (Bobby Johnson), the smart and introverted Warren (Ali Hadji-Heshmati), and the socially-conscious Jinx (Laura Marcus).

While Alfie enjoys a good relationship with Fraser, he clashes with the school's deputy headteachers, beginning with the strict disciplinarian and fascistic Isobel Pickwell (Michelle Gomez), who fakes her death.

The Class K pupils are: Recurring characters include: Other notable guest characters who were the focus of episodes included India (Phoebe Waller-Bridge), a drug counsellor; and Kevin Schwimer (Kyle Soller), a fraudulent History teacher who competes with Alfie for the affection of Class K. The special revival episode featured most of the original cast of pupils, with the exception of Alexander.

Bernadette Hoburn (Vicki Pepperdine) is introduced as the blunt, strict new headmistress of Abbey Grove; Horne reprises his role as Fraser, but it is explained that he accepted a promotion to working in the school's kitchens.

[citation needed] Rotten Tomatoes gave the show 71%; a critic said, "the script is patchy and the story is too silly for its own good but there are enough laughs to make this a hit with the target audience"[21] The revival series received a mixed reception.

[22] In The Guardian, Jack Seale gave the series two stars, calling it "juvenile", "still lack[ing] any coherent structure or purpose", and a "pointless revival", but "slightly better" than the original show and "not as obviously empty-hearted".