This is from the Texas Education Agency's 2010-2011 reporting. These are SAT averages of the Class of 2010 by school district - so seniors who graduated or should have graduated in May 2010 - for only the reading and math portions of the test. For some reason, the writing portion of the SAT is not included. I tossed in a few charter schools which are public schools, and a few private schools. I would add more private school SAT scores, but they are hard to find since those scores are not reported to the TEA.
SAT average - school district (ISD)/private or charter
1402 - Cistercian (private boys)
1393 - St. Marks (private boys)
1355 - Hockaday (private girls)
1196 - Highland Park
1194 - Ursuline (private girls)
1192 - The Alexander School (private)
1179 - Westlake (charter)
1161 - Southlake Carroll
1153 - North Hills (charter)
1155 - Coppell
1152 - Plano
1110 - Fort Worth Academy of Fine Arts (charter)
1104 - Richland Collegiate (charter)
1101 - Lewisville
1093 - Argyle
1092 - Sherman
1090 - Grapevine-Colleyville
1088 - Celina
1086 - Lovejoy
1080 - Allen
1077 - Prosper
1074 - Waxahachie Faith Family (charter)
1073 - McKinney
1072 - Rockwall
1066 - Granbury
1053 - Frisco
1050 - Keller
1044 - Howe
1042 - Richardson
1041 - Midolthian
1040 - Van Alstyne
1032 - Melissa
1026 - Gunter
1026 - Denton
1026 - Hurst Euless Bedford (HEB)
1016 - Lake Dallas
1015 - Denison
1010 - Arlington
1009 - Ennis
1008 - Carrollton-Farmers Branch
1007 - Sanger
1006 - Forney
1003 - Greenville
999 - Wylie
995 - Garland
993 - Anna
991 - Crandall
991 - Red Oak
991 - Royse City
989 - Mansfield
977 - Corsicana
965 - Waxahachie
964 - Princeton
959 - Treetops (charter)
958 - Mesquite
946 - Grand Priarie
946 - Pottsboro
945 - Little Elm
945 - Duncanville
938 - Irving
924 -Quinlan
916 - Winfree (charter)
915 - Evolution Academy (charter)
910 - Terrell
903 - Advantage Academy (charter)
898 - Ferris
877 - Life School (charter)
860 - Dallas
859 - Peak Prep (charter)
855 - Cedar Hill
852 - A+ Academy (charter)
849 - DeSoto
839 - Pegasus (charter)
822 - Universal Academy (charter)
784 - Dallas CAN Academy (charter)
799 - Lancaster
748 - Gateway (charter)
713 - Dallas Faith Family Academy (charter)