The main difference with the CFI qualification is not just having a good understanding of aeronautical knowledge and being able to fly to the required standards, but being able to convey the information to the student. Every student is different and it is important that the instructor is able to adapt his teaching style to each individual student. Particularly with initial flight training, the instructor should cultivate a secure training environment and give constant support, encouragement and feedback to the student.
Federal regulations require the applicant to hold at least a Commercial License. The usual oral and practical test with an FAA examiner are required, but with CFI you need to complete two written tests, one testing your aeronautical knowledge, the other the Fundamentals of Instruction (although if you have a teaching qualification this can be waived).
The student will receive intense ground instruction on all aspects of teaching and the student will need to compile their own lesson plans and lecture/teaching notes to successfully teach the appropriate subjects. The student will learn to plan lessons with time constraints and to put across the information on the whiteboard.
The student will take the position of the instructor in the aircraft and will learn to articulate and instruct each maneuver with a demonstration to the instructor, who will be acting as the student. This environment is set up so that the student will begin to recognize common mistakes he or she may encounter during training.
This level is the final preparation for the student and the instructor will assess the student's ability to explain aerodynamics to a prospective student on the ground and in the air as well as their knowledge of the Fundamentals of Instruction, which they will be tested on in the oral portion of the FAA checkride.