The first part of reprimanding an employee constructively is focusing on the behavior or issue, not the employee themselves. Reprimands that focus on employees tend to not achieve anything because they tend to be too general and tend to not include any solutions. “What were you thinking?” is an example of such a reprimand. They have a greater likelihood of causing damage to the employees’ confidence than doing any real good. Instead, give data and example(s) on the behavior or issue, while using pronouns like “we” or “us” instead of just “you.”
Next, make sure that reprimands are always private. As unpleasant as reprimands are for either party, the employee or the manager, they become drastically more unpleasant if it’s done in a public or group setting. Whether it’s the additional peer-pressure that will come from the reprimanded employee’s colleagues afterward or the potential for pushback/insubordination against the manager, just don’t do it. The issues between a manager and employee are between them and nobody else; other than potentially other groups that are required to be notified like HR.
Lastly a reprimand becomes drastically less effective if it happens too far after the fact. Make reprimands in a timely manner so the employee will be more likely to remember the issue or behavior instead. Logically it becomes harder to justify the reprimand from the managers’ perspective if it happens too late because the employee will think “if the issue was so important, why it come up sooner?” Managers should especially avoid delayed reprimands right before performance reviews are given to reduce the likelihood they just brought up the issue so the company wouldn’t have to pay out as much of an annual raise/bonus.