Hi Mary,
My 6 year old just participated in the
Jedi Training Academy (JTA) at Disney's Hollywood Studios a couple of weeks ago and LOVED it! When we were there, they were holding registration under the Star Tours sign in what would have been the queue if the attraction wasn't currently undergoing a major reimagining. There were several Cast Members there who were directing potential Padawans participants to the registration area. It wasn't anything fancy or well-marked, just a Cast Member with a clipboard but they got the job done very efficiently. So while the actual sign up location may vary, it will be held in an area near the JTA stage.
You are correct, all participants (ages 4 - 12 years old) must be present along with an adult to register. This is so that they can ask the kids a couple of questions to make sure they can follow some basic directions. They will then be given a slip with their name and time of training session they are scheduled to participate in that day.
The number of participants is limited and they start registration first thing in the morning and stop once the spots are filled for the day. You are correct again, these spots usually fill up fast, especially during peak seasons so for anyone who wishes to participate, I recommend heading over to sign up as soon as DHS opens.
Wishing you many magical memories :-) Allison