Changing from straight adopt to foster.... how hard is it?

Does anyone know the percentages of children that are reunified with their parents ? I know that this is always the goal , but what are the actual statistics? Is it like 70% are reunified or something different? We are wanting to foster with the hopes of eventually being able to adopt. Are our chances better if we are foster parents than with straight adoption? Our Cw says thats true , but I just want to make sure that we are getting the truth and she's not just telling me that because she wants us to become foster parents.