Dynamically Inserting A List In WHERE Clause Of A Query

What I need?: A way of dynamically inserting a list in the WHERE clause of a query. (in the form, WHERE ID = 1,2,3,6,9 etc)

Imagine an example DB with 3 columns Student ID, Name, Teacher_ID. (Lets assume Teacher_ID with value 100 means its the Headmaster)

I need to create a list with Student ID's, who are directly/indirectly under the Headmaster. Example:

Headmaster
Teacher 1 (ID 200)
Teacher 2 (ID 250)
Student 1 (ID 300)
Director
Teacher 4
Student 5

In the above example, since I only want those students/teachers under the headmaster, either directly/indirectly, my list would contain Teacher 1, Teacher 2, and Student 1. (In my case, just their ID's, so 200, 250, 300)

Director, Teacher 4 and Teacher 5 wouldnt be in the list since theyre not directly/indirectly Headmaster.