How much does a guardian at litem have to do with the outcome of custody?

Obviously, in any case where a party knows that the other party is not being truthful, there is an issue of how to "prove" that they are not being truthful.  If there is some evidence that will disprove the statements being made then you and your attorney have to get that evidence and then decide when and how to present it. If a party is not telling his/her attorney the truth, that puts the party in a potentially precarious position-- should the truth come out.  If a party is not telling the guardian ad litem the truth and the guardian discovers that later, it can never be a good thing for the deceptive party.  However, the guardian's main concern is what is in the best interest of the children, even if their parents may not be truthful. Therefore the issue may be "What was the parent untruthful about?"