PTS concepts Vs ACS concepts
https://www.faa.gov/training_testing/testing/test_standards/media/FAA-S-8081-6D.pdf
PTS Concept
The Flight Instructor Practical Test Standards are designed to evaluate competency in both knowledge and skill.
The FAA requires that all Flight Instructor practical tests be conducted in accordance with the appropriate Flight Instructor Practical Test Standards and the policies set forth in the Introduction. The flight instructor applicant must be prepared to demonstrate the ability to instruct effectively in all Tasks included in the Areas of Operation of the appropriate practical test standards, unless otherwise noted.
https://www.faa.gov/training_testing/testing/acs/media/commercial_airplane_acs_change_1.pdf
ACS Concept
The goal of the airman certification process is to ensure the applicant possesses the knowledge, ability to manage risks, and skill consistent with the privileges of the certificate or rating being exercised, in order to act as pilot-in- command (PIC).
During the ground and flight portion of the practical test, the FAA expects evaluators to assess the applicant’s mastery of the topic in accordance with the level of learning most appropriate for the specified Task. The oral questioning will continue throughout the entire practical test.
The flight portion of the practical test requires the applicant to demonstrate knowledge, risk management, flight proficiency, and operational skill in accordance with the ACS.