You don't need to prepare much. You already know the facts. They will do some testing, which you can't prepare for, and ask about family history. You may want to make sure you have information about your family history. Other than that you most likely know everything you need to know about your case - you will just be providing them with that information, and taking some tests, which as I have indicated, you can't prepare for.
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You probably should at least consult with an experienced family law attorney BEFORE the evaluation meeting and the next hearing. What you need to present, and how you need to present it, will depend on many things, including:
what custodial arrangement has been in place,
what custodial arrangement you want,
what custodial arrangement the OTHER parent wants,
who's proposing the change,
and why the change is proposed,
what the child(ren) wants, if he or she is of an age for their wishes, and the reasons for their wishes to be considered,
and other facts.
A 730 evaluator is there to assist the court in gathering information to help the judge figure out what custody arrangement is in the best interest of the child. You need to figure out what arrangement you want that is consistent with the child's best interest, and how to get that information to the judge. An experienced family law attorney will have assisted dozens, and possibly hundreds of clients in similar situations.
You should consider consulting with Mr. Gould-Saltman. I think you should be able to paint the picture pretty clearly in a day and a half, with an evaluator who has experience and knows what to look for and what to inquire into.
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