I beg to differ! He may be a "supervisor," but due to his potential, he is asked to "act" in a managerial capacity. His performance in his acting capacity is also going to matter while deciding if he is good enough to be a "manager."
It is always the "performance" that needs to be PRIMARILY appraised. His behavioral traits, etc., may (in fact, should) be appraised as well, but the determinant will be the efficacy of his managerial skills, attitudes, and perspectives.
Therefore, if his predominant role in his present assignment is "managerial" and if he has been asked to "act" in that capacity as such, then he ought to be appraised as a manager (giving due consideration to the fact he is not yet a "manager" but is on the way to becoming one).
To address my own difference in approach, I suggest that a "special" appraisal be carried out in such cases since this is not a normal assignment. A way can be found out. In any case, a supervisor, in many ways, is close to managing! He is just a little away from the actual process of managing.
Regards,
Samvedan
September 15, 2011