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2.
The Juniors and Seniors of a high school they are attending. In other words, eleventh and twelfth graders.

Often they are feared the non-upperclassmen, usually freshmen.
Eleventh Grader: YES! We're eleventh graders! That makes us upperclassmen!!!
Ninth Grader: Uh-ohh.... I'm afraid of getting in the way of an upperclassmen....
by xairbearx June 29, 2009
 
1.
(high school) Upperclassmen are the 2 highest grades of high school. The Juniors, and the seniors. Juniors and Seniors are the big grades of high school. Sophomores are not yet upperclassmen but they're more respected than Freshman. Freshman look up to upperclassmen. Many Freshmen feel intimidated by upperclassmen. But its good for the Freshman to *try* to get on their good side.
The Upperclassmen and the Freshman.......(STORY)

Freshman: "Hey whats up? I heard theres a party tonight, can you tell me where its at?

Junior: Um...Your a freshman right?

Freshman: "Yeah"...

Junior: AAAHAHAHAHAHAHAHA!

THE EEENNNDD!!
by FlyLikeABird July 19, 2009
 
3.
Any student in a high school other than a freshman. These students are usually pretty normal, but for some of them, the evolution from frosh to non-frosh makes them into total jackasses. These jackass-upperclassmen should be avoided by freshmen at all costs.
Upperclassman: Hey, you're a freshman, right?
Freshman: Uh ... yeah?
Upperclassman: Go clean the floor with your tongue.
by Duskmoon December 14, 2008
 
4.
people who are "upperclassmen" aren't immature 9th graders. they are seniors and juniors, or the top grades in a school. everyone other than the youngest. freshman in high school are not upperclassmen, and shouldn't call themselves upperclassmen. 6th graders are basically the same social status as 9th graders, if not better.
"wow 7th grader you can't be mean to me. you're talking to an upperclassmen"-freshman
"actually you arent cool and your a freshman, not an upperlcassmen. you aren't a senior or junior, yeah your not coool."-7th grader and the rest of the world
by sg_em_rb_ninthgraders_BFF2 March 14, 2010
 
5.
noun meaning one who is always right and should be respected.
"A freshman tried to tell me I was wrong, but when I pointed out that I am an upper classman, he conceded that I must therefore be correct."

chuck norris was an upper classman even when he was a freshman.
by necrocandy January 07, 2010
 
6.
10th, 11th, and 12th graders. Most of which make fun of 9th graders.
Upper Classmate: Yeo freshmeat!

Freshman: uhhmm.. *quivers*

upper classmen
by Danielle d. l. August 19, 2008
 
7.
10th,11th,and 12th graders in high school who think they have the right to be complete assholes and be jerks to all of the freshman just because they have been there longer.
upperclassmen:freshman suck!
freshman:your dating one....
by sarahhhhhhhhhhhhh May 20, 2007