We went through mediation. As stepmom I did not have to attend. I was afraid I wouldn't be able to, but before dh went in they asked if there was anyone he wished to have with him (could be lawyer, his mom, etc), so he said me, of course and we did it. I'm not sure what would have happened if the biomom had objected (though, at that point, she probably would have if she could, and she didn't so maybe it wasn't an option). I say expect little.
I expected they would listen to us and give suggestions as to how to make a compromise. They did not. We told our story. They left to talk to biomom, they came back, told us what she said. We responded, they left and talked to her, then came back. We still disagreed on visitation and they said, well, then go to court. I'm sure there are better mediators out there. I just expected them to have suggestions or something, but really they just said, "she said x" "you say Y" "you disagree." Duh. But we went. They interviewed dss, too, though I 'm not sure why, as they had no say in anything and seemed to contribute very little! Not a bad experience, just not very helpful. I hope there are more helpful ones out there.