Kaya Scodelario was included in Entertainment Weekly's 2009 "Summer Must List", being named "Bad Girl" for her portrayal of Effy.

"[2] Until the first series' eighth episode, "Effy", she does not speak at all, instead sitting silently in the background of the scenes in which she appears, usually with a cold stare or a wry smile.

In her first speaking appearance, she describes how she feels toward others: Sometimes I think I was born backwards... you know, come out of my mum the wrong way.

Various psychologists who have studied Effy's character and personality have come to the conclusion she may have suffered from selective mutism, in Generation 1 and 2, something that affected her in the later seasons.

After expressing her feelings of misanthropy to Tony, however, her brother snidely remarks to her that she "doesn't fool [him]", suggesting that she is more vulnerable than her guarded and apparent aloofness may lead others to believe.

She also proves to be perceptive and sly, as she almost single-handedly mends both Tony and Michelle's and Sid and Cassie's romantic relationships, a task that seemed essentially hopeless.

Despite her usual composure, she goes "off the rails" after her parents' separation and the love triangle between her and her classmates Freddie McClair and James Cook, once close friends before their rivalry over Effy pushed them apart.

Though they reconcile, when she leaves treatment in her centric episode, it is shown she is being abused by her obsessive psychiatrist and his unconventional hypnotic methods for treating her; Dr. Foster attempts to make Effy "forget" her friends.

Her favorite film is E.T..[6] Her best friend is odd girl Pandora Moon, who despite their differences, "gives the detached and cool Effy a heart".

Effy on the other hand has taken on the role of a parental figure somewhat, where she is seen washing and drying her and Tony's clothes (albeit ineptly), and watching after her mother.

Back at home Tony receives a parcel from Michelle, which is actually the watch he gave her for her birthday, prompting him to become further frustrated with Sid.

Effy, with Pandora in tow, picks up weed at Cassie's where she enquires about her relationship with Sid, but otherwise doesn't probe the subject.

As for Sid, Effy sends an acquaintance of hers called Jake to Cassie's – knowing the chances that they would sleep together – and takes a series of photos through the window.

At school, Effy doesn't use Sid's artwork he created for her (she lets Pandora use it), but explains to her teacher that her GCSE Art coursework is conceptual, in which she used an array of emotions – referring to her recent experiences helping others mend their relationships.

[citation needed] In the first episode of the series, Effy catches the eye of best friends Freddie, Cook and JJ on her first day at Roundview College.

When Freddie attempts to engage in conversation with Effy, flirtatiously suggesting possibly more than a friendship, she warns him that his best friends Cook and JJ want the same, which will likely complicate things.

Effy excuses herself from class, prompting Cook to follow, where they light up a spliff and the two have sex in the school nurse's office.

Effy, seeing the impact she had had, is apologetic and, although she cannot guarantee that she will stop, she expresses sentiment that she would like to become his friend after he admits that he loves her too, and is somewhat hurt when he refuses.

When the group goes camping in an area of the woods known as Gobblers End, the uninvited Cook shows up and bitterly reveals secrets, including that he and Pandora have apparently been sleeping together behind Effy's back.

JJ, who wins the race, takes charge and demands that they solve their problems once and for all, forcing both boys to admit that they each love Effy and telling her that she must choose between them.

Over the summer, Effy goes with her mother to Italy, breaking up with Freddie due to the guilt she feels from the pain she caused Katie and Cook and does not contact anyone.

Eventually, Effy begins acting erratically, cutting out pictures of death and pasting them to her mother's bedroom wall while mentioning "creatures" coming for her.

Effy is once again institutionalised, although refusing to go back under the supervision of John as it is apparent he has been using hypnotic methods to cause her to forget everything about her past and life.

When Freddie tries to leave, the door is locked and John, brandishing a baseball bat, reveals that he wants Effy for himself, explaining "she really does love you, you know."

In the two-part episode "Fire", set three years after the ending of Series 4, Effy, now 21, is living in London with Naomi, with whom she now has a close relationship, and working a dead-end job as a receptionist in a high-profile hedge fund.

After achieving success through illicit information provided to her by Dominic, she pursues a relationship with Jake (Kayvan Novak), her wealthy boss, and begins to live the high life.

Unfortunately, this is short-lived when the Financial Services Authority receives a tip-off and evidence that her success was the result of insider trading, and Jake places the blame squarely with her (although he had actually encouraged her to do it).

Effy manages to get Emily back to London to ensure that Naomi's last days will be spent with her beloved girlfriend at her side.

Effy's story ends with her being placed into a police car to be taken into custody, her trademark wry smile crossing her face.

"[11] Ann Harper Covington of Strike Magazine explains: "Effy’s character became the embodiment of something many teens related to at the time: an adolescent battling a mental disorder and not always using the best tools to do it.