The film The Paper Chase (1973) involved a Harvard-type law school. Professor Charles W. Kingsfield, Jr. (played by the actor John Houseman) said to his first-year law students:
 
“The study of Law is something new and unfamiliar to most of you—unlike any schooling you have ever been through. We use the Socratic Method here. I call on you, ask you a question, and you answer it. At times you may think you have reached the correct answer. I assure you that is simply a delusion on your part. You will never find the ultimate, correct, and final answer. In my classroom there is always another question—there is always a question to follow your answer. You teach yourself the law—but I train your mind. You come in here with a skull full of mush and leave thinking like a lawyer!”
 
The popular image developed of all students—not just law students—coming to school with “skulls full of mush” that a teacher and an institution can shape to have proper learning. Conservative radio talk show host Rush Limbaugh has said many times that liberal teachers believe that they can take their students’ “skulls full of mush” and educate them into becoming liberal thinkers and Democrats.
 
   
The Internet Movie Database
The Paper Chase (1973)
Professor Kingsfield: You come in here with a skull full of mush and you leave thinking like a lawyer.
 
23 December 1973, Seattle (WA) Times, “‘Paper Chase’ one of the season’s brighter films” by John Hartl, pg. G1, col. 6:
“You come in here with a head full of mush, you leave thinking like a lawyer,” Houseman says. In the end, Bottoms recognizes that knowledge is indeed power, and that this is his true reward for study.
       
Google Books
Final Dress
By John Houseman
New York, NY: Simon and Schuster
1983
Pg. 493:
The study of Law is something new and unfamiliar to most of you—unlike any schooling you have ever been through. We use the Socratic Method here. I call on you, ask you a question, and you answer it. At times you may think you have reached the correct answer. I assure you that is simply a delusion on your part. You will never find the ultimate, correct, and final answer. In my classroom there is always another question—there is always a question to follow your answer. You teach yourself the law—but I train your mind. You come in here with a skull full of mush and leave thinking like a lawyer!
 
Google Books
Television’s Second Golden Age:
From Hill Street Blues to ER
By Robert J. Thompson
Syracuse, NY: Syracuse University Press
1997
Pg. 84:
Though at leas some college education had become commonplace for many segments of the population, best-selling books like Allan Bloom’s The Closing of the American Mind (1987) and E. D. Hirsch’s Cultural Literacy (1987) argued that we entered the educational system with our heads full of mush and left it in much the same state.
 
RushLimbaugh.com
Hollywood Fills Sculls Full of Mush with Radical Environmentalist BS
July 25, 2008
(...)
RUSH: Ted Turner started Captain Planet. It was all about the militant environmentalists blaming corporate America. These cartoons, of course, targeted for young little crumb-crunchers and skulls full of mush out there.
 
Google Books
Crisis in Our Classrooms:
The Lies We Tell Our Children
By Jim Murphy
Bloomington, IN: CrossBooks
2011
Pg. 17:
Rush Limbaugh, noted radio talk show host, refers to children as “little skulls full of mush,” meaning that their minds (rational thinking, if you will) aren’t fully formed yet.
 
Media Matters for America
Limbaugh: “College Is Where Liberals Get Hold Of Young Skulls Full Of Mush”
Video ››› May 25, 2011 4:37 PM EDT ››› MEDIA MATTERS STAFF
From the May 25 edition of Premiere Radio Networks’ The Rush Limbaugh Show: ...
   
RushLimbaugh.com
Rutgers Coach Can’t Bully Players, But Left-Wing Professors Can Bully Christian or Conservative Students All Day Long
April 05, 2013
(...)
RUSH: (...)  And, by the way, stigmatized, pointed at in class if they hold Christian or conservative values, mocked, laughed, made fun of, because everybody knows the intent of modern propagandists—educators—today is to beat those ideas out of young skulls full of mush.