It is important to identify the weaker performers in your organization but managers tend to grade people too highly and this can make the process difficult to implement. One good way around the problem is to force a bell curve on your managers.
A standard bell curve distributes a small percentage (10 – 15%) at the top and bottom and the remainder in the middle. To force the bell curve, tell your managers that they must evaluate their people in one of three categories, Top Middle and Bottom….and that they must distribute them 15% in the top, 70% in the middle and 15% at the bottom.
For a staff of 20 employees in one class this would translate neatly into 3, 14 and 3. If you end up with fractions, change the percentages and round the numbers you present. Even if the percentages work out (they usually don’t) you should always give your manager(s) actual numbers rather than percentages as this reduces pushback.
You can do this exercise with as few as 10 employees where you might ask for 2 top, 6 middle and 2 bottom and then rank the 2 bottom against each other.