A fascinating thing happens midway through “The Rehearsal,” Alison MacLean’s adaptation of Eleanor Catton’s novel about a year in the life of acting students: you realize that the movie has been getting a lot of mileage out of interweaving “real world” scenes and acting class exercises, so that you aren’t immediately sure what kind of scene you’re looking at; consequently, you become determined to figure out how to tell one from the other instantly, but the movie keeps fooling you. Which isn’t to say that this is a film built entirely around tricks of perception—just that it has a firm grip on its central idea: that for actors, life and performance are a bit of a blur. MacLean and her screenwriter Emily Perkins capture all this in an ensemble movie set mainly at an acting school in Auckland, New Zealand. The school is ruled by a gifted and demanding acting coach named Hannah (Kerry Fox of “An Angel at My Table,” who tucks the film into the back pocket of her comfortable jeans and strolls off with it). She keeps pushing the students to take risks, find the truth, stop being so afraid of what others think of them. Some of her advice seems helpful and undeniably useful, but she also seems to encourage the sort of shorthand “intimacy” and “intensity” that results in a lot of cliche acting, as well as poor behavior by actors. Which is to say that she’s complicated—more so than many of her students, who are too great in number for the film to really get a handle on them as individuals. MacLean and Perkins envision “The Rehearsal” as a “year in the life movie,” unfolding in a series of scenes that often feel like truncated tableaux you’d encounter in live theater. Sometimes the movie cuts into them in such a way that you mistake them for “real” interactions, and there are points when the characters are interacting in the outside world and you wonder if that, too, is an acting class exercise (the movie has fun toying with our perceptions, particularly in a scene that looks as if it’s about to turn into a male-male pickup on a busy street). The problem is that the relatively brief running time (less than two hours) works at cross-purposes with the movie’s laid back characterizations and populated cast. Alan Parker’s 1980 film “Fame”—to which “The Rehearsal” is being compared, for obvious reasons—also tried to do too much with too many characters in too brief a running time, but it compensated by letting the actors be big, and go right up to the edge of caricature. None of the actors in this film’s cast really get a chance to pop except for James Rolleston (of “The Dark Horse”), who as Stanley, a first year acting student, becomes the film’s de facto lead. Rolleston’s portrayal of an Aboriginal actor with daddy issues, an insinuating charm, and a nearly sociopathic knack for turning life into drama gives the movie something resembling a center; but it’s not enough to counter the feeling that you’re seeing a film that probably should’ve been a TV series, the better to accommodate all the subplots, none of which are developed in the detail they deserve.Stanley has an affair with an underage student, Isolde (Ella Edward). Isolde has a 15-year-old sister, Victoria (Rachel Roberts), whose affair with her tennis coach George Saladin (Erroll Shand), caused him to be accused of rape (whether violent or statutory is never clear). George becomes the object of a media scandal that continues to unfold throughout the film. Although there’s potentially a lot to say about the role of acting during a public shame-fest, “The Rehearsal” never convincingly teases out the connections between this stuff and all the bits in the acting school—although there are tasty glimpses of a theater piece the students are working on; it feels like a drily funny send-up of the kinds of cliched pieces that theater students mount in response to news events they aren’t really interested in, except as material for their work. There are another half-dozen characters, mainly young actors, who get a few scenes each but never coalesce into memorable persons. It’s hard to tell whether the film is too bighearted to ruthlessly narrow its focus or if it was a much longer film that got cut down, losing emotional connective tissue. Whatever the explanation, “The Rehearsal” is a sensitive, thoughtful, often provocative movie that nevertheless feels like a missed opportunity. The movie is at its best when it’s sitting in class watching the students work through material and their own issues. In fact these sorts of scenes are so consistently strong (particularly when Fox’s coach is alternately cheering and goading them) that I wouldn’t have minded a more abstract, conceptual movie set entirely in the classroom. MacLean hasn’t made a theatrical feature in 18 years, but she’s directed lots of scripted television, including excellent episodes of “Sex and the City,” “Carnivale” and “The Tudors.” Her last theatrical movie was “Jesus’ Son,” an adaptation of Denis Johnson’s book that I believe is one of the greatest and least appreciated dramas of the ’90s. Despite its problems, this new one is a welcome return, but it ultimately feels like a rehearsal for something grander.