Ms. Darbus is the theatre teacher at East High and is also Gabrialla and Troy’s homeroom teacher. In the first HSM, she is the one that recognizes the talent that Gabriella and Troy have. Ms. Darbus instructs Kelsey to mentor them and teach them the song thatthey sing at their call backs. Ms. Darbus is kind of under the control of Sharpay 
because Sharpay has always been very involved in the drama club. Ms. Darbus is tricked by Sharpay to change the day of the call back to the day of the basketball championship and the academic decathlon. Despite this, Troy and Gabriella able to make it to the call back and nail their song.
Ms. Darbus first sees Troy as a basketball jock. She doesn’t realize that he actually has a hidden passion for the theatre. In the first HSM, Ms. Darbus gives Troy and Chad detention and forces them to decorate props for the drama club. This is one of the first times Troy has been exposed to something other than basketball. This changes him and he is open to new experiences. Ms. Darbus was the 
one that introduced him to theatre and because of this I think Ms. Darbus is very important in the development of Troy throughout the HSM movies.
In the third HSM, there is an opportunity for one student at East High to receive a scholarship to the Julliard School of Performing Arts. In order to be offered this scholarship the students have to apply. Ryan, Sharpay, Kelsey, and Troy are all informed that they will be given a shot at the scholarship. This confuses Troy because he didn’t submit an application. This really makes Troy think and question his future and what he wants to do. At the end of the third movie, Troy goes to East High late at night to release all of his thoughts and confusion. Here he finds Ms. Darbus. She explains to him that she submitted his application to Julliard because she saw how much theatre filled him up. Although Troy doesn’t go to Julliard, he picks a college where he can do theatre and play basketball. This is thanks to Ms. Darbus. 
Were all in this together 