Yes, when you enter the park for your PPO H&V reservation there will also be a Cast Member holding a sign that reads "Jedi Academy". You go just past Hollywood and Vine check-in to do Jedi sign-ups. If there are several in your family, have someone stay to check in for breakfast and another adult (plus the Jedi child to participate) over to sign ups. Works smoothly!
Processes are subject to change, but typically as the children file in there are two lines. The "back" line when viewed from the audience (or the "right" line when viewed from the back of the line) traditionally files up the stage steps to Darth Vader. Nothing is guaranteed, and the kids are asked to line up themselves, usually by height for best viewing of every student on stage.