This is a work in progress. Check back every so often to see if changes have been made. I’ll put an asterisk next to anything I’ve added after the latest “version” date. This is version 12.03.2025.
Teaching adults a second language, or developing a good teaching app/program, requires both a solid grounding in the “why” (theory/research) as well as the “how.” If you don’t understand the why, you have no way of knowing if the how is working, or how to fix it when it doesn’t.
It is easy to think that, after listening to a single lecture or reading an explanation of second language acquisition (SLA), you’ve “got it” and are ready to move on to building your code or drawing up your lesson plan. Sadly, it isn’t that simple. There are lots of variables and potential problems in picking up a new language, and if you don’t have a firm grasp of the theory and evidence on how we acquire languages, your attempt to teach it will fail.
I can’t emphasize this point too much: Don’t try to rush ahead after the first flush of comprehension. What will happen—and I’ve seen this dozens of times—is that you will start to “fill in” gaps in your knowledge about things with your own personal experience or “intuition.”
Now, there are still many questions for which we don’t have good answers in SLA, times when a teacher or researcher has to go “beyond” current evidence. And there’s nothing wrong with that, as long as you (1) understand what we DO know already, and (2) have several years of reading, research, and teaching to back that intuition up.
I don’t claim you need to read everything on the following list. I also don’t agree with everything that appears in all of these sources, especially on the “Application” list (more on this below). But if you want an understanding of most of the moving parts of language acquisition and teaching, reading all of these sources will get you about 80% of the way there.
The core of this list consists of works written or inspired by the father of modern second language acquisition theory, Dr. Stephen Krashen (who was my Ph.D. advisor and, later, occasional co-author). Many of these can be found for free on his generous personal website.
I’ve listed them very roughly in the order in which I’d assign them for a college class in teaching second languages, but there is a lot of overlap in the topics. Don’t skip sections that seem to you like “review”! It’s not review. You’ve learned things in the meantime that will give you a deeper understanding of the things you encountered earlier in your reading.
There is obviously a great deal about the topic of teaching that is not on this list. I’m trying to focus on what is most useful to language teaching. For a more general book on the psychology of learning, see Frank Smith’s Comprehension and Learning: A Conceptual Framework for Teachers (1975) (Archive.org copy).
Theory/Research
(1) Krashen, S. (1981) Principles and Practices in Second Language Acquisition.
Still the core text after 45 years. Read the whole thing. Twice.
(2) Krashen, S. (1985) The Input Hypothesis.
Krashen answers his critics and applies the theory to several key questions. Read the whole thing. (Also on Archive.org).
(3) Krashen, S. (1985). Inquiries and Insights: Selected Essays.
Addresses some specific issues, partial overlap with some topics in #2 but it’s a good review. Can skip chapters 3 and 6, but the rest are worth reading. (Copy also on Archive.org).
(4) Krashen, S. (1981). Second Language Acquisition and Second Language Learning.
A series of papers published the same year as P&P, with overlap with #1 but some additional insights into a few important issues. After having read the three books above, all the chapters should be comprehensible (and interesting!) to you, but focus on chapters 1-4.
(5) Krashen, S. (1984). Writing: Research, Theory, and Applications.
Helps you understand the nature of writing and reading. (Copy on Archive.org). Can skim sections and dip in where things look interesting.
Reading these five books, all published in the 1980s, will give you a solid foundation on Krashen’s theory. What follows are additional aspects of research and theory that round out the picture. Several of these are articles written by Krashen and other researchers working with him.
(6) Krashen, S. (1991). “The pleasure hypothesis.” In GURT Proceedings.
Another excellent review and application of the theory to various issues in language teaching, with a good review of some applications (covered more in full in reading below). Again, do not skip the sections that seem like “review” to you! The more you read them, the more the ideas will sink in. Sinking in is good.
(7) Smith, F. (1988). “How education backed the wrong horse” in Joining the Literacy Club.
Beginning at least by the early 1990s, when I first met him, Krashen referred to his “Input Hypothesis” as the Comprehension Hypothesis, part of a wider concept pioneered by reading researchers Ken Goodman and Frank Smith. Anything you read by Smith is worth your time if you’re a parent or teacher, but this particular chapter summarizes the errors of behaviorism in teaching (think Duolingo).
The very best case for error correction is in writing, and Truscott shows that even there, it isn’t helpful. This is an important article to understand fully why error correction in any form is not a good method of instruction. You need to understand the strength of the case against certain traditional practices by looking at the actual evidence.
Krashen added “compelling” to his description of the kind of input we need for language acquisition. This two-page paper is a good example of that.
(10) Krashen, S. (1998). Comprehensible output. System, 26.
Krashen rebuts some mistaken notions of the role of output (speaking, writing). Again, you need to understand how to apply the theory to ideas that may at first glance appear to be reasonable, but in fact are not supported by the theory or the data.
An excellent review of why alternatives to comprehension language teaching methods are ineffective. Again, it is important to understand why certain guiding principles used in traditional classrooms are wrong in order to prevent falling into those same traps in designing effective approaches.
This is an example of going “beyond” the research, but based on years of deep thinking and research on a topic. If he is correct (and I think he is), most accent training is a waste of time.
(13) Krashen, S. (2004). “Applying the Comprehension Hypothesis: Some Suggestions.” IJFLT, 1.
An excellent, brief application of the theory to a number of important concerns in language teaching, plus an update on some research.
(14) Krashen, S. (n.d.) “Down with forced speech.”
A short paper outlining why forcing students to speak before talking “emerges” is a bad idea.
It’s important to understand the nature of vocabulary acquisition and the levels needed for different types of text. Nation has been the key researcher in this area for the past 40 years, and this paper supports the notion that that, with enough reading (CI), all of the vocabulary needed for adult-level reading is acquired over time and without explicit instruction. (Hint: Once you understand how words are incrementally acquired through repeated exposure in context, you have the building blocks of organizing a comprehension-based curriculum.)
Cummins outlines a few key concepts in understanding how the first and second language relate, including BICS, CALP, and underlying language proficiency. While written for a bilingual education audience, this paper is important for second language teachers as well.
All fields of language education—bilingual education, second language, ESL, reading—rest on the same foundations. Krashen is one of the few scholars who understands this. Yet to this day, researchers in these fields remain largely ignorant of what other language educators are doing.
Application
None of the applications of “comprehension-based” teaching are perfect or complete. The goal in reading these sources is to start understand how language can be made comprehensible, to develop a “toolbox” of strategies, and to form the right instincts for knowing what will and will not work. By seeing how others have done it, you can begin to adopt and adapt these strategies to your setting (online, video, classroom, etc.). The ideal scenario for you would be to teach students with these approaches (after getting lots of “input” in how they should be taught) to see how these approaches work and what their strengths and weaknesses are.
(1) Asher, J. (1977). Learning another language through actions: Total Physical Response.
Asher’s method and research to support it were done in advance of the Krashen’s theory. You can skim over his theoretical musings and focus on understanding how he made input comprehensible. You don’t need to go through every chapter. Read the overview and a few of the early lessons, and then search for some examples online to see how it works in a classroom. Archive.org copy.
(2) Winitz, H. The Learnables.
This isn’t a text but a link to a very short sample of Harry Winitz’s commercial course (his did write a book on his approach, but it currently is prohibitively expensive on Amazon). Click on a language you don’t know (I tried Hebrew) and you’ll see a few short samples of how it works.
Originally, these were printed materials with cassette tapes in the 1970s (?), I believe. I had a copy years ago. The important thing is to see how he uses a very simple visual approach to making the input comprehensible. At later stages (too late, IMO), very short stories are used.
(3) Krashen, S., & Terrell, T. (1983). The Natural Approach.
This is the key “application” text for comprehension approaches. Read it twice, like Principles and Practices. In many ways, the techniques and strategies discussed in The Natural Approach form the foundation for most of the approaches that followed.
A very limited glimpse at some NA strategies can be found on this very useful site at BYU. The BYU site has other short demonstrations of different methods you should also take a look at, including many traditional approaches.
(4) Brown, M., & Palmer, A. (1988). The Listening Approach: Methods and Materials for Applying Krashen’s Input Hypothesis.
This book is nearly impossible to find outside an academic library, but I can’t exclude it from the list given its importance in the history of comprehension-based teaching. It outlines an approach used in Thailand to teach Thai with two teachers in front of the class instead of one. It is a creative application of CI and worth checking out if you can find examples or descriptions elsewhere (visit an academic library near you, or perhaps try for an interlibrary loan with your local library?).
Brown later used the term “Automatic Language Growth” for his method, and there is still a website that contains links to videos of approach using Thai. This one is supposed to be Level 1. Notice how the two teachers are in constant conversation/dialogue. (You need to have patience to put up with a good deal of incomprehensible input in this example, which I think is a real weakness of this video. I didn’t have the patience to find a better example on their site.)
(5) Krashen, S. (2004). Applying the Comprehension Hypothesis: Some suggestions. IJFLT.
Krashen applies the theory to some specific instances, with a good update on certain research questions related to teaching.
(6) Krashen, S. “The case for narrow listening.” System, 24 + “The case for narrow reading.” Language Magazine.
Both “narrow” reading and listening are excellent ways of getting good comprehensible input and taking advantage of background knowledge in language acquisition.
(7) Seely, C., & Ray, B. Fluency Through TPR Storytelling.
There are several editions of this book, and the method has apparently evolved a bit over the years, de-emphasizing the TPR aspect. But it has always been essentially a storytelling approach, and as such, is a huge advance over many previous approaches. It wasn’t the first method to take storytelling seriously, of course. Many traditional methods used short stories designed specifically for students, even if they were not the main focus in the classroom. Bill Van Patten’s Destinos series (shown on public television in the 1990s) was a soap opera designed to teach Spanish.
TPRS created an entire movement in American secondary schools, and has been one of the most successful in getting CI approaches into classrooms. As with other methods, it would be very helpful for you to find some examples online of its implementation. This workshop handout is also useful, but requires a bit more fleshing out to really understand what TPRS is all about.
One take on how and if you should check for comprehension in a classroom.
This is inspired in part by the TPR Storytelling approach, but drops the TPR and goes instead for a repetition of the story, with gradual expansion. I’m not certain it is the best approach, but it is driven by getting students “hooked” into a story as a way of delivering compelling input over time. Read it with that aim in mind.
Short and to the point, as the best Krashen papers are.
(11) McQuillan, J. (2006). iPod in Education: The Potential for Language Acquisition. Apple.
This white paper was written at the request of Apple to explain the possibilities of the (then new) iPod in language classrooms. In it, I review some basic principles of applying the CI theory to audio and video materials.
This is a short paper on applying the insights from Paul Nation’s work (and some of my own research) to getting someone from upper beginner to advanced in English as a second language (or any other language, of course). Reading is in fact one of the cheapest, most efficient sources of CI available, and yet is still widely underutilized even by comprehension-based methods.
(13) Krashen, S. (1997). Foreign Language Education: The Easy Way.
This short volume is also hard to find, but it presents several of the ideas presented in the previous readings in summary form. It makes a nice reference of approaches and strategies, so worth having. Again, re-reading about these topics is encouraged. You’ll get more out of each exposure (like vocabulary acquisition!). Copies are available on US Amazon and probably elsewhere.
Follow Us!