The film takes place in the waning days of a supposedly disappointing summer. School approaches with its constrictions, and it seems the only way to really escape now is to have a sleepover. Thus, many such gatherings are held, and everyone around is going to one or the other, with a few people roaming, searching desperately for fun and (possibly) love.
Most of the characters are well shaded, leaving those that aren't sticking out (such as the new girl who stumbles into trouble probably due to her being under the influence of alcohol) like sore, stereotypical thumbs. That being said, Mitchell manages to elicit at least a couple good moments in all of the different passages. A few times, he strikes gold, like when he makes the brilliant choice of cutting between girls and boys talking about the same memory. Or when he has a difficult confession play out in a way adeptly designed enough to distract you from the (possible) blatancy of the situation. (Judging from photos on IMDb, he bears a resemblance to this character, a troubled college grad; perhaps the scene is drawn from personal experience. Much of the film could be.)
The various parties range from the interior type where people play games and watch porn to the exterior style where people swim, dance, and lounge on the shore and on rowboats. The latter is supposedly better suited for those who are older, but, as one guy at that party muses, sometimes older teens wish they could go back to the more juvenile days. This is what the title refers to, that people grow old without wanting to be where they used to be (this isn't true). Not, as some have thought, that kids don't really drink or do drugs at parties (they do, according to this film).
Mitchell is a talented scenarist who, if he works out the minor kinks in his writing, has the potential to make some incredible films. He's got the technical facets down, with an eye for lighting and a feel for music (knowing for the most part how to employ potentially cloying music). Even if it falls slightly short of greatness, "The Myth of the American Sleepover" is memorable, with engaging incidents and characters. B+