No, you cannot counsel a LT no more than a SPC can counsel a SGT. The best method is to sit down and discuss things from a mutually supported position. You two are a team. If you state he does not follow orders, are you saying he is disobeying the Commander? If so this is a problem. If he is disobeying your advice, it is not the same as disobeying an order. The LT is ultimately responsible for the platoon, and as such is the final decision authority for the platoon. The goal is that a LT learns from the experience of a seasoned Platoon Sergeant, but in the end the Platoon Sergeant is required to obey the orders of his Platoon Leader as long as they are: legal, moral, and ethical.