Instruct the wise and they will be wiser still; teach the righteous and they will add to their learning.
NIV
Give instruction to a wise man and he will be yet wiser; teach a righteous man (one upright and in right standing with God) and he will increase in learning.
AMP
Give instruction to a wise man, and he will be yet wiser: teach a just man, and he will increase in learning.
KJV