Poor Mary! John has just attacked the standard of her without giving her any idea of where she is going wrong; on top of that he＇s repeated the criticism in front of another member of staff. 
By using some of the suggestions below, see if you can rewrite the dialogue so that John offers Mary constructive and positive criticism that will help her to improve her performance:
Invite Mary to a private interview 
Ask if she is ready to discuss the standard of her work 
Acknowledge the fact that she is new to the company and that there is a lot to learn 
Say that her reports are lacking in detail and accuracy 
Ask her if she is aware of that 
Say that she is often late in the morning 
Ask her if there are personal problems that make it difficult for her to arrive on time 
Say that some of the clients she deals with have complained that she misses appointments 
Ask her if she can explain why this is 
Ask her if there is anything you can do to help her improve in these areas. 
Set a date for another talk in a few weeks to review her progress.
If John conducts the interview along these lines, Mary will:
Know exactly which aspects of her work are unsatisfactory 
Will have the opportunity to explain why she has problems 
Will not be publicly humiliated 
Will feel that she is getting support in her efforts to improve.

Reference
Brenda Townsend Hall,1998
www.ecglink.com