This has been updated for 2014-2016 here:
http://dallas-area-schools.blogspot.com/2014/02/2014-2016-uil-reclassification-and.html
The 2012-2014 reclassification and realignment for football and basketball was announced on 2-2-2012. Here are the Dallas-Fort Worth area schools:
High school student enrollments for each level:
5A - 2090 and up
4A - 1,005 to 2,089
3A - 450 to 1,004
2A - 200 to 449
1A - 199 and below
Below 100 - cutoff for 6 man football
5A
5A Region 1, District 3
Arlington
Arlington Bowie
Arlington Houston
Arlington Lamar
Arlington Martin
Ft. Worth Paschal
North Crowley
Weatherford
5A Region 1, District 4
Haltom City Haltom
Keller
Keller Central
Keller Fossil Ridge
Keller Timber Creek
N. Richland Hills Richland
Northwest
Southland Carroll
5A Region 1, District 5
Coppell
Denton Ryan
Lewisville
Lewisville Flower Mound
Lewisville Hebron
Lewisville Marcus
5A Region 1, District 6
Carrollton RL Turner
Colleyville Heritage
Euless Trinity
Grapevine
Hurst Bell
Irving
Irving MacArthur
Irving Nimitz
5A Region 1, District 7
Cedar Hill
De Soto
Duncanville
Grand Prairie
Mansfield
Mansfield Timberview
Midlothian
South Grand Prairie
5A Region 2, District 9
Jesuit
Dallas Skyline
Dallas Sunset
Dallas WT White
Richardson
Richardson Berkner
Richardson Lake Highlands
Richardson JJ Pearce
5A Region 2, District 10
Allen
McKinney
McKinney Boyd
Plano
Plano East
Plano West
5A Region 2, District 11
Garland
Garland Lakeview Centennial
Garland Naaman Forest
Garland Rowlett
Garland Sachse
North Garland
South Garland
5A Region 2, District 12
Longview
Mesquite
Mesquite Horn
North Mesquite
Rockwall
Rockwall-Heath
Tyler Lee
4A
4A Region 1, District 5
Azle
Denton
Denton Guyer
Lake Dallas
Northwest Nelson
White Settlement Brewer
Wichita Falls
Wichita Fallas Rider
4A Region 1, District 6
Chisholm Trail
FW Boswell
FW Carter-Riverside
FW Dunbar
FW Eastern Hills
FW North Side
FW Polytechnic
N. Richland Hills Birdville
Saginaw
4A Region 1, District 7
Aledo
FW Arlington Heights
FW South Hills
FW Southwest
FW Trimble Tech
FW Western Hills
Fw Wyatt
Granbury
4A Region 1, District 8
Burleson
Burleson Centenntial
Cleburne
Crowley
Everman
Joshua
Waco
Waco University
4A Region 2, District 9
Frisco
Frisco Centennial
Frisco Heritage
Frisco Liberty
Frisco Wakeland
Lewisville The Colony
Little Elm
Prosper
4A Region 2, District 10
Carrollton Creekview
Carrollton Newman Smith
Highland Park
Forney
Mesquite Poteet
North Forney
Terrell
West Mesquite
4A Region 2, District 11
Dallas Adamson
Dallas Carter
Dallas Kimball
Dallas Molina
Dallas Pinkston
Dallas Seagoville
Dallas South Oak Cliff
North Dallas
4A Region 2, District 12
Dallas Adams
Dallas Conrad
Dallas Hillcrest
Dallas Thomas Jefferson
Dallas Lincoln
Dallas Samuel
Dallas Spruce
Dallas Woodrow Wilson
4A Region 2, District 13
Denison
Greenville
Lovejoy
McKinney North
Royse City
Sherman
Wylie
Wylie East
4A Region 2, District 15
Arlington Seguin
Ennis
Lancaster
Mansfield Lake Ridge
Mansfield Legacy
Mansfield Summit
Red Oak
Waxahachie
3A
3A Region 1, District 6
FW Diamond Hill-Jarvis
Kennedale
Lake Worth
Mineral Wells
River Oaks Castleberry
Springtown
3A Region 2, District 9
Bridgeport
Decatur
Gainsville
Krum
Sanger
3A Region 2, District 10
Argyle
Aubrey
Carrollton Ranchview
Celina
Frisco Lone Star
3A Region 2, District 11
Dallas Wilmer Hutchins
Dallas Madison
Dallas Prime Prep Academy
Dallas Roosevelt
Ferris
Irving North Hills
3A Region 2, District 12
Anna
Bonham
Melissa
Neveda Community
Princeton
3A Region 2, District 14
Crandall
Emory Rains
Kaufman
Quinlan Ford
Wills Point
2A
2A Basketball
2A Basketball Region 2, District 11
Bells
Callisburg
Howe
Pottsboro
Sadler S&S Consolidated
Tom Bean
Whitesboro
Whitewright
2A Basketball Region 2, District 12
Caddo Mills
Farmersville
Gunter
Leonard
Pilot Point
Sunnyvale
Van Alstyne
2A Basketball Region 2, District 13
Dallas Faith Family
Dallas Life Oak Cliff
Eustace
Kemp
Malakoff
Palmer
Red Oak Life
Scurry-Rosser
2A Football
2A Football, Division 1, Region 2, District 5
Bowie
Boyd
Callisburg
Paradise
Pilot Point
Ponder Whitesboro
2A Football, Division 1, Region 2, District 6
Caddo Mills
Commerce
Farmersville
Howe
Pottsboro
Sunnyvale
Van Alstyne
2A Football, Division 1, Region 2, District 7
Eustance
Gand Saline
Kemp
Lone Oak
Malakoff
Quitman
Winnsboro
2A Football, Division 1, Region 3, District 12
Clifton
Godley
Grandview
Maypearl
Palmer
Red Oak Life
Whitney
2A Football, Division 2, Region 2, District 6
Blooming Grove
Corsicana Mildred
Dallas Life Oak Cliff
Millsap
Rice
Rio Vista
Scurry-Rosser
Tolar
2A Football, Division 2, Region 2, District 7
Bells
Gunter
Leonard
Sadler S&S Consolidated
Tom Bean
Whitewright
1A
1A Basketball
1A Basketball, Division 1, Region 2, District 14
Arlington Summit Int'l Prep
Dallas Gateway
Dallas Triple A Academy
Grand Prairie Advantage Academy
Italy
Itasca
1A Basketball, Division 2, Region 3, District 20
Avalon
Grand Prairie Harmoney Science Academy
Irving Universal Academy
Milford
Waxahachie Advantage
Waxahachie Faith Family
1A Football
1A Football, Division 1, Region 2, District 6
Cayuga
Dallas Gateway
Italy
Itasca
Kerens
Malakoff Cross Roads
6-Man Football
6-Man Football, Division 1, Region 3, District 12
Irving Universal Academy
Saint Jo
Savoy
Waxahachie Advantage