Here are some books and blog posts that either deal with Herbartian educational philosophy, or mention him in connection with Charlotte Mason.
"An Oyster and a Jewel: Johann Herbart and Charlotte Mason. (~ A Study of Charlotte Mason's Principle #10 ~), by Lynn Bruce. (Ambleside Online website)
"On Herbartian Unit Studies" (AfterThoughts blog)
The Stress of Education (Sage Parnassus blog)
Lynn Hocraffer's discussion of CM Principles, scroll down to discussion of #9 and #10. "Herbart was a major German Education Philosopher - I had to read much of him in my own college training. Herbart is VERY popular in modern circles - the idea that the "How" is more important than the "What" extends not only through the children's education but also through the teachers! It is considered that a teacher can teach anything by simply knowing the method."
Charlotte Mason In Memoriam, Part IV (Ambleside Online website)
"Herbart and his fellows shaped their philosophy of education to meet the conditions of the bookless school. They supplied a sanction for the procedure which the facts had forced upon the Training College. Although there are very many more books to-day than there used to be, they are still too often cheap 'readers' so constructed as to demand no real effort of the child. The outlook and the methods of the Training College are much more liberal than they were, but the old idea that the child cannot work without the constant intervention of the teacher still underlies the system. The teacher must still talk endlessly. Inspectors, as he knows, will require it of him, and will judge him by his capacity to do so. Method is still all important. We start with the axiom, as Miss Mason says, that "what a child learns matters less than how he learns it," with the result that he is "in danger of receiving much teaching with little knowledge." The child who has once tasted freedom knows the difference."Introduction to the Herbartian Principles of Teaching, by Catherine Isabel Dodd, 1901. The original source of the infamous "Robinson Crusoe Concentration Scheme" described by Charlotte Mason.
The Educational Theories of Herbart & Froebel, by John Angus MacVannel, 1905
The Herbartian Psychology applied to Education, by John Adams (quoted in Towards a Philosophy of Education, Chapter VII)
"[Charles] De Garmo's article, "The Herbartian System of Pedagogics," in The Educational Review (1891) significantly influenced the introduction of Herbart's philosophy to Americans." De Garmo also wrote a book, Herbart and the Herbartians.
Tompkins, Arnold. Herbart's Philosophy and Educational Theory, in Educational Review, October, 1898.
And a note on Tompkins' article from The School Journal - Volume 57 - Page 399, 1898: "Arnold Tompkins contributes to the Educational Review for October an article on Herbart's philosophy in which he has the bad grace to pummel a corpse; for Herbart's philosophy is as dead as the old Puritan conception of Satan."
Okay...I think we're done here.