Yesterday I wrote about praising in public. The other half of the standard is to correct in private.
We can all remember a time when we took a public chewing-out, or at least were uncomfortable bystanders to one. The primary result when that happens is resentment; behavior change may follow but only out of avoidance, not from any positive motivation.
Far better to pull your people aside when you need to criticize. Technically "private" means behind closed doors, somewhere no one can see. The intent, though, is to attract as little notice as possible, and sometimes pulling someone into your office has the opposite effect.
Think of it this way: What you're really trying to do is protect the reputation of your team member. You want improvement without making him or her feel less capable, and without making the rest of the team doubt that team member's contribution.
Sometimes a quiet conversation right there at the work station is the least obtrusive, so long as no one can overhear. Or maybe you want to go for a walk, or ask an employee to stop by on the way back from break or lunch. There are a lot of ways to engineer a conversation that will pass unnoticed by the rest of the group.
That makes your job easier, too, because you can zero in on performance and the employee can listen and speak without worrying about his or her image. If you're encouraging where it's warranted, and you make correction relatively low key, then you get the change you want without all the drama. That's good for both of you.