this is probably an old post....but will respond anyway. Get information re: your area...while I did my training to fost-adopt as my goal is adoption and not straight fostering....my county does not like working with agencies and will place with them last....this is not only limited to prospective adoptive parents.
Their rationale....they feel as though they prepare people/couples better than agencies do, and they've had previous bad experiences with FFA homes in our county....
BUT....as I've read and talked with different people, this is NOT the case or scenario everywhere, and your decision needs to be made regarding where you live and the dynamics of county/agency.
Good luck either way.

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Speech therapist to 39 children
6/1/09, homestudy officially approved
6/3/09, Selected!

....decided not to move fwd. after disclosure meeting
9/29/09, Selected!
10/6, appears relatives applied for ICPC
current status: Selected for 6 month old girl