http://texasthespians.org/ Everything that students and parents need to know about Thespians and the state festival can be found on this link.
http://summerstockaustin.org/ Summerstock Austin is for high school and college students. This program produces professional musicals. The students learn everything from theatre management to Broadway style choreography. Acceptance is based on auditions and is FREE!
http://www.vortexrep.org/ THE VORTEX Repertory Company The Vortex offers a scholarship based summer youth program. The Vortex also produces a professional show that is free to the students that are accepted after auditioning.
I have tons of information on summer camps, excellent options, but they are too many to list here.
http://zachtheatre.org/ Zack Scott Theatre in Austin! We had amazing experiences there with their production of RENT!