Stephen Krashen is a professor emeritus at the University of Southern California, where he taught linguistics.

He comments here in response to an earlier post about the Common Core standards:

What this excessive detail also does is
(1) dictate the order of presentation of aspects of literacy
(2) encourage a direct teaching, skill-building approach to teaching.
Both of these consequences run counter to a massive amount of research and experience.

There is very good evidence from both first and second language acquisition that aspects of language and literacy are naturally acquired in a specific order that cannot be altered by instruction (C. Chomsky, 1969, The Acquisition of Syntax in Children from 5 to 10. Cambridge: MIT Press; Krashen, S. 1981, Second Language Acquisition and Second Language Learning, Pergamon Press, available at http://www.sdkrashen.com).

There is also very good evidence that we acquire language and literacy best not through direct instruction but via “comprehensible input” – for literacy, this means reading, especially reading that the reader finds truly interesting, or “compelling.” (Krashen, S. 2010.The Goodman/Smith Hypothesis, the Input Hypothesis, the Comprehension Hypothesis, and the (Even Stronger) Case for Free Voluntary Reading. In: Defying Convention, Inventing the Future in Literacy Research and Practice: Essays in Tribute to Ken and Yetta Goodman. P. Anders (Ed.) New York: Routledge. 2010. pp. 46-60. Available at http://www.sdkrashen.com)