How significant were African Americans in shaping the progress of Reconstruction?

This is a matter of a great deal of debate.  No one really knows for sure.

The most common answer today is that the freed slaves were very important in shaping life after the war.  They are given credit for reestablishing family structure that had been hurt by slavery.  They are given credit for starting black churches that would become a pillar of the black community.

They are not, however, usually portrayed as having had much to do with the government of the South during this time.  This is a backlash against previous views of the subject that said that governments in the South were terrible because they were controlled by blacks who lacked the education and experience to be good legislators.  Today, most historians see Reconstruction as a failure and they tend to lay the blame at the feet of whites, both Northern and Southern.

Some scholars, notably Thomas Holt (himself African American) argue that blacks did have a great deal of influence in government as well.  Holt argues that black elites are to blame for the problems of other blacks because they looked down on the lower class blacks and did not do much to help them.

Overall: most historians give credit to blacks for shaping their own lives but do not blame them for the problems of Reconstruction.  (You can see this approach in the first answer posted here.)  Some revisionist scholars have started to argue that black elites, at least, deserve more blame than they get.