I wonder how to uncerstand the sentence 'these agencies are usually relied upon too exclusively" in the following passage :

   To achieve this internal control through identity of interest and understanding is the business of education.While books and conversation can do much, these agencies are usually relied upon too exclusively. Schools require for their full efficiency more opportunity for conjoint activities in which those instructed take part, so that they may acquire a social sense of their own powers and of the materials and appliances used.

            source:  summary of Chapter Three: Education as Direction,from Democracy and Education,by John Dewey. 

e2efour 

   When I first read agencies, I thought of something like an advertising agency.But the meaning is more like means of or aids to learning). He ways that too much importance is given to the use of books and conversation, to the exclusion of other aids.

The style of this book (published in 2016) is somewhat old-fashioned.
Here is what one reviewer said about Dewey:
   "Dewey's writings can also be difficult to read, and his tendency to reuse commonplace words and phrases to express extremely complex reinterpretations of them makes him susceptible to misunderstanding. So while he held the role of a leading public intellectual, he was often misinterpreted, even by fellow academics." (http://www.wikiwand.com/en/Democracy_and_Education)

 Cagey 

  It is this meaning of agency:

"Agencies" refers to books and conversation.
In Dewey's opinion, books and conversation are helpful, but people usually depend on them 'too exclusively'. That is, people depend on them to do everything, but other things are needed as well.

As other people have said, this writing is difficult to follow, but I believe that Dewey goes on to suggest that students should also have a chance to work together, using what they have learned.

PaulQ 

On this sentence, "these agencies" refers "books and conversation"
The word agency is used in its sense of "means; provider; something (or someone) that produces a particular result, etc."