Submitting evidence in court

It is almost certain that the other side will object to the letter as hearsay, which it probably is.  They also may object on authenticatin grounds - how does the Court know that your son actually wrote the letter?  You may be able to overcome the authenticity objection if you are familiar with your son's handwriting, or saw him write the letter. Hearsay is an out of court statement offered in evidence for the truth of the matter asserted.  As a general rule, hearsay is not allowed in evidence, although there are many exceptions.  The basic policy is that a judge or jury is better able to determine whether someone is telling the truth if they can observe him/her testifying, and listen to him/her being cross-examined.  I assume that you would want the letter admitted in the hopes that the Judge will believe its contents, but the Judge would be better able to determine if the letter is true if he could see your son testify and hear your son's answers during cross-examination.  There are many exceptions to the hearsay rule.  Without knowing the circumstances or the contents of the letter, I can't say whether one might apply, or whether there is some other reason why the Judge may allow it into evidence.  However, if the Judge felt that your 17 year old should not be in Court for the custody hearing, to me that implies that the Judge felt that he should not be a witness. There are obvious parenting reasons why you may not want your son involved in this matter.  Assuming that you do, however, from a strictly legal point of view, I don't see what  you have to lose by trying to get the letter admitted into evidence (unless the Judge has instructed you not to get your son involved, in which case having him write the letter could be considered contempt of court and get you in big trouble.)