School districts generally decide which staff they will assign to complete FBAs. It might be a school psychologist, a behavior specialist, or a special education teacher. Often, the process starts with a team discussion about which behavior is the greatest concern, who will observe the student in order to take data about that behavior, and when and in what settings they will take the data.
Special education rules require that evaluations be completed by a person with the necessary experience and qualifications. The more complicated the behavior, the more likely it is that a specialist may be needed to help understand the functions of the behavior and identify effective interventions.