Thanks Luis...ha ha.
11-14 is a tough age group compared to a 5-9 because they are hitting the age where they "think" magic is not cool and the "think" they know how every effect is accomplished. It is the preteen age group. Sometimes some of the guys will show off and shout things out and throw challenges your way more so than young girls who will give you great reactions. This is because they want to show off and draw attention to themselves to impress their peers.
It is crucial to let them know that you are performing magic WITH them and NOT AT them.
As far as effects I would look at items like: Chicago Opener, Invisible Deck Routine, A torn and restored Routine, ACR, Anything with Loops (check your lighting), 20th century silks, Stratosphere, Scotch and Soda, Fiber Optics - Rope Routine (I don't do Professor's Nightmare - see notes below) Book Tests work well, Magic Square Routine, Anything with Fire is a Bonus for this age group, Needle through Arm, Pressure. I am just throwing ideas out there. You want the magic to be a step up from the "kiddie" stuff - if that makes sense.
Stay Away from the younger age group effects like: Stop Light Cards, Forgetful Freddie, Magic Coloring Book, Break Away Wand, D'Lites, Stuffed Animal or Puppets, etc. Some of these classics have been seen by that particular age group when they are younger and you'll get the "We've Already Seen This One!" from numerous kids. Don't get me wrong...they are great tricks but mainly for the typical birthday parties we perform for the 5-9 year olds.
If you have any particular / specific questions feel free to ask.
Be weary of effects that might make fun of someone. This is a double edged sword for that age group. You may lose your audience if you make someone look like a fool up in front of their peers. Or...I've seen it go completely the other way and everyone is laughing including the volunteer. Be careful.