The Ultimate Quotable Einstein by Alice Calaprice lists this as "probably not by Einstein". However, this post from quoteinvestigator.com http://quoteinvestigator.com/2014/04/29/common-sense/ traces it to a reasonably plausible source: the second part of a three-part series by Lincoln Barrett (former editor of 'Life' magazine) titled "The Universe and Dr. Einstein" in Harper's Magazine, from May 1948, in which Barrett wrote "But as Einstein has pointed out, common sense is actually nothing more than a deposit of prejudices laid down in the mind prior to the age of eighteen." Since he didn't put the statement in quotes it could be a paraphrase, and "as Einstein has pointed out" makes it unclear whether Einstein said this personally to Barrett or Barrett was recalling a quote of Einstein's he'd seen elsewhere. In any case, the interview was republished in a book of the same title, and Einstein wrote a foreword which praised Barrett's work on the book, so it's likely he read the quote about common sense and at least had no objection to it, whether or not he recalled making the specific comment.
Unsourced variant: Common sense is the collection of prejudices acquired by age eighteen.
Disputed
“Common sense is the collection of prejudices acquired by age eighteen.”
“There is nothing more uncommon than common sense.”
Anonymous saying, dating back at least to its citation in Natural Theology (1836) by Thomas Chalmers, Bk. II, Ch. III : On the Strength of the Evidences for a God in the Phenomena of Visible and External Nature, § 15, where the author states: "It has been said that there is nothing more uncommon than common sense."; it has since become misattributed to particular people, including Frank Lloyd Wright.
Misattributed
“It has been said that there is nothing more uncommon than common sense.”
Natural Theology (1836), Bk. II, Ch. III : On the Strength of the Evidences for a God in the Phenomena of Visible and External Nature, § 15; though provided without attribution of author, the saying "There is nothing more uncommon than common sense" has since become misattributed to particular people, including Frank Lloyd Wright.
“Nothing can be more contrary to religion and the clergy than reason and common sense.”
Rien n'est plus contraire à la religion et au clergé qu'une tête sensée et raisonnable. — Paul-Henri Thiry, Baron d'Holbach, Théologie portative, ou Dictionnaire abrégé de la religion chrétienne (1768): Folie
Misattributed
“I offer nothing more than simple facts, plain arguments, and common sense.”
1770s, Common Sense (1776)
Saturday Review, 17, 1864, pp. 129–30
1860s
“Our best theories are not only truer than common sense, they make more sense than common sense…”
The Fabric of Reality (1997)
Salon interview (1997)
Context: I'm always astounded at the way we automatically look at what divides and separates us. We never look at what people have in common. If you see it, black and white people, both sides look to see the differences, they don't look at what they have together. Men and women, and old and young, and so on. And this is a disease of the mind, the way I see it. Because in actual fact, men and women have much more in common than they are separated.
I. 2, 71b.9 sqq
Posterior Analytics
Letter 8
On the Aesthetic Education of Man (1794)
