Although DawsonCasting is frequently ridiculed, mocked, and parodied, there are actually many practical reasons for this trope's usage.
# Labor laws and regulations apply to acting just as they do to any other profession. There is a whole string of laws that child actors are subject to. This includes (in the UK and the USA) education requirements as well as restrictions on work hours. These conditions are rarely convenient when one is trying to meet the deadlines for finishing a film or a TV season.
# Many countries require a parent or a legal guardian to be present whenever a child actor is on the set. It is challenging enough arranging for a child to take many weeks off school to appear in a film or television program; asking their caregiver to sacrifice the same amount of time as well is even more difficult.
# The vast majority of professional actors are adults anyway, so if you hold an audition for a teen role, 90% of the actors you see will be over 19, and they will be the ones with good [=CVs=].
# Teenagers are less capable than young adults of effectively handling the pressures of stardom. Furthermore, a teenager is far more likely to leave a show after one season (or a film series after one entry) to focus on their education.
# It is easier to tell a teenager apart from a young adult if you yourself fall into either one of these age categories. Professional casting directors are usually middle-aged or older. To them, a 16-year-old does ''not'' look noticeably younger than a 21-year-old.
# Puberty tends to be fickle. An adorable 14-year-old can transform into a gawky, gangly 16-year-old with rather shocking celerity, and even [[SheIsAllGrownUp grow up into a walking fanservice repository]] by the time they are 18. Furthermore, most movies and TV programs are not filmed in the order that is shown on screen, so you could have someone leave a building as a child, appear outside looking like a teenager, then become a child again when they re-enter the building. This inconsistency will not happen if the actor has already completed puberty.
# Television programs and movies tend to be filmed over several months and, in some cases, ''years''. Child actors run the risk of outgrowing their characters and, due to puberty, an 18 year old can look very different from a 15 year old. [[NotAllowedToGrowOld The age gap between a 20 year old and a 23 year old, on the other hand, is not as conspicuous]].
# While animated characters present fewer problems, teen voices, particularly male ones, still break without much warning. Therefore, even if an actor is capable of emulating their younger voice at a later age, recording sessions become complicated. Adult voice actors, especially female ones, do not have to deal with this difficulty, and are usually more experienced anyway.
# [[PaedoHunt Obscenity and child porn laws]]; as per these regulations, it is generally illegal to show even simulated sex on film[[note]]And in many countries, even in animation.[[/note]] unless all of the involved individuals are at least 18 years of age. Having adults play the characters allows the filmmakers to depict various behaviors on camera that would get them arrested if even one of the actors turned out to be 17 or younger.
# Dawson Casting permits {{fanservice}} as well as [[ComedicUnderwearExposure some forms of humor]] without running into trouble. In most countries, the above laws forbid not just child nudity, but also sexualized depictions of minors, which is just enough of a wild card to worry filmmakers. An underwear shot, for example, can come across as a "sexualized depiction" even if that was not the true intention.
# Most successful teen actors -- i.e., the ones with the most experience and impressive resumes -- are the child equivalents of Dawson Casting. This is because, compared to actual children, teenagers are more able to remember lines, and are less likely to [[NeverWorkWithChildrenOrAnimals go completely off the rails on some random whim]].
# Many actors who start their careers as children or teenagers do so because of [[PushyStageParent stage parents]], who not only cause long-term psychological harm, but are also considered a nuisance for filmmakers, as they frequently butt in and [[WagTheDirector try to dictate]] various parts of the production.
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This trope works better with females than with males. Most shows focus on the actors' faces, and while girls can keep a very similar facial structure and vocal range even after going through puberty, boys tend to have a significantly deepened voice and a facial stubble, which is faintly visible even if it is shaved. Therefore, a man in his twenties or a boy in his late teens playing a 15-year-old is less believable than a woman or a girl within the same age ranges playing a 15-year-old. For example, look at Austin St. John from ''Series/MightyMorphinPowerRangers'', at age 18, playing a high-school freshman. [[http://a3.ec-images.myspacecdn.com/images01/31/63039052fc135e5f1bed3aa4349a0ace/l.jpg It doesn't look right.]] Now look at Creator/AmyJoJohnson, older than Austin at age 22, playing a character on the same show, also a high school freshman. [[http://images4.fanpop.com/image/photos/22800000/amy-jo-johson-amy-jo-johnson-22845809-1024-768.jpg It's noticeably less obvious.]]