If your primary purpose is to close a performance gap, think carefully before choosing participants. Some might not need the training and resent having to attend. For instance, if a group of employees needs help with writing, do not include those already working up to the desired standard in a basic writing course.
They will more than likely not want to be there. Furthermore, if only one person has a performance gap, think about whether you are using training instead of coaching or counseling. Addressing the problems of one employee as if they are the problems of a group is a recipe for disaster.