APTA has a number of documents on the appropriate use of personnel and PT/PTA teamwork. Professional standards would first ask that you follow the law. To answer the question of what is appropriate practice from a legal perspective, you should review your state practice act for physical therapy. The requirements for the use of personnel in physical therapy can vary widely from state to state.
When you review the regulations for your state, look carefully at the definitions for the different physical therapy personnel covered and how supervision is defined and applied. Review information on state licensure and practice acts.
APTA Policies & Procedures on Supervision
Supervision and Medicare
PT/PTA Teamwork
Cotreatment