The complex model, a three-stage process, places dynamic reflection between the input and the output. The mentor needs to work with the trainee to establish an input–output process that is functional and sophisticated. Targets are set, and usually these are appropriate specific, measurable, attainable, realistic, time indicated (SMART) targets to underpin the trainee's development. The mentor should enable and encourage the trainee to evaluate and improve their teaching. Senior mentors, sometimes known as professional mentors, are often already senior staff members with weighty, whole-school responsibilities. The senior mentor in a secondary school may be the main conduit for training innovation and communications. A particularly young mentor may encounter some resistance, and may need help in establishing working relationships. Experience and maturity are mentoring assets. Teachers with only a few years of experience may have much to offer, but some occasionally report difficulties.