What are the best short films?

I work at a school and considering showing one or two short films to secondary school students. The films should appeal to 11 to 16 year old. Ideally the films should be about short length maximum 35 to 40 minutes. I know there are very few movies at this length so shorter movies length suggestion will be welcomed.

Thank you in advance

Show them Tale of Tales and then tell them to interpret it and laugh at them racking their brains.

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Look, I'm not judging you - after all, I'm posting here myself, but maybe, just maybe, if you spent less time here and more time watching films, maybe, and I stress, maybe your taste would be of some value. Just a thought, ya know.

Here's a link to an IMDB list of short movies. Some are very short - 6 min - but you may be able to find some that suit.

http://www.imdb.com/search/title?title_type=short

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“The Universe is under no obligation to make sense to you.”
― Neil deGrasse Tyson

thank you will give it a go

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"Anything less than immortality is a complete waste of time."

A few suggestions that might be appropriate:

The man who planted trees - 30 minutes
http://www.imdb.com/title/tt0093488/?ref_=sr_1
　
Harvie Krumpet - 23 minutes
http://www.imdb.com/title/tt0382734/?ref_=fn_al_tt_1

Ménilmontant - 38 minutes
http://www.imdb.com/title/tt0147039/?ref_=fn_al_tt_1

Paperman - 7 minutes
http://www.imdb.com/title/tt2388725/

2081 - 25 minutes
http://www.imdb.com/title/tt1282015/

Apichatpong Weerasethakul makes a lot of really great short films, I recommend checking out Phantoms of Nabua and A Letter to Uncle Boonmee. Both are pretty easy to find online but if you want I could send you links.
Here are the IMDb pages though:
A Letter to Uncle Boonmee: http://www.imdb.com/title/tt1480648/
Phantoms of Nabua: http://www.imdb.com/title/tt1585269/?ref_=fn_al_tt_1

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Mubi

Chris Marker's 'La Jetée' is the first that comes to mind, one of my favorite films of all time. 28 minutes. Also, a subtitled version of the entire film is available on YouTube so you can easily evaluate if it'd suit your purposes.

Can't post links yet, will edit this later but it's on imdb /title/tt0056119

La Jetee?

Some that spring to mind:

La Jetee
Night and Fog
Oedipus Wrecks/Life Lessons (Allen/Scorsese's New York Stories segments, skip Coppola's if you know what's good for you)
Franz Kafka's It's a Wonderful Life
Paperman
Kitchen Sink
Spielzeugland (Toyland)
Duck Amuck
Harvie Krumpet
The Singing Trophy
Cigarettes and Coffee
More
The Red Balloon
Bambi Meets Godzilla
Fresh Guacamole (PES' work in general is great)
A Trip to the Moon
La Luna
Walkshort
The Fantastic Flying Books of Mr. Morris Lessmore
The House is Black
Un Chien Andalou
La Luna
Presto
The Ventriloquist
Envelope

The Simpsons: The Longest Daycare is better than a lot of modern Simpsons episodes.

Paperman was fantastic.

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