You will find schools that have grades from 9th to 12th in this  listMagnet schools listed below includes grade levels from PK3 through 12th grade.

Academy of Aerospace and Engineering, South Windsor
Grades: 6 to 8  Theme: STEM

Academy of Science and Innovation, New Britain
Grades: 6 to 12 Theme: Arts  

Capital Preparatory Magnet School, Hartford
Grades: PK3 to 12 Theme:

Classical Magnet, Hartford
Grades: 6 to 12 Theme:

Connecticut River Academy, East Hartford
Grades: 6 to 12 Theme:  

Global Experience Magnet School, Bloomfield
Grades: 6 to 12 Theme:

Great Path Academy at MCC, Manchester
Grades: 9 to12 Theme:

Greater Hartford Academy of Arts High School - Full Day, Hartford
Grades: 9 to12 Theme:

Greater Hartford Academy of Arts High School - Half Day, Hartford
Grades: 9 to12 Theme:

Kinsella Magnet School of Performing Arts, Hartford
Grades: PK4 to 12 Theme: Arts

Metropolitan Learning Center for Global and International Studies, Bloomfield
Grades: 6 to 12 Theme: International Baccalaureate

Pathways Academy of Technology and Design, East Harford
Grades: 9 to 12 Theme:

Sport and Medical Sciences Academy, Harford
Grades: 6 to 12 Theme: STEM

University High School of Science and Engineering, Harford
Grades: 9 to 12 Theme: STEM