This is part of the Teenage Kicks season at the BFI and also screens on August 22nd. Details here.
Time Out review:
A wicked black comedy about teenage suicide and pernicious peer-group pressure, this refreshing parody of high-school movies is venomously penned by Daniel Waters and sharply directed by Lehmann. The Heathers are three vacuous Westerburg High school beauties who specialise in 'being popular' and making life hell for socially inadequate dweebettes and pillowcases. Having sold out her former friends in these categories, Veronica (Ryder) becomes an honorary member of the select clique - but turns monocled mutineer. Aided by handsome rebellious newcomer JD (Slater), she devises a drastic plan to undermine the teen-queen tyranny, but underestimates JD's ruthlessness: the scheme backfires dangerously. The compromised ending (forced on the film-makers by New World) is a serious let-down, but there is some exceptional ensemble acting, several stylish set pieces, and more imaginative slang than you could shake a cheerleader's ass at. More crucially, the film uses an intimate knowledge of teen-movie clichés to subvert their debased values from the inside.
Here (and above) is the trailer.