Textbook Review and Discussion of CK-12

As a pre-service teacher, my initial reasoning for seeking a digital textbook was admittedly expediency.  I thought that there would be difficulty in acquiring a printed textbook and I wanted to see if digital would be easier to procure.  What I found during my search, however, was something I was very excited to investigate and analyse.  I discovered the non-profit organization CK-12, whose tagline “Open, flexible education for a better tomorrow. Today!” is representative of its purpose.  CK-12 provides open source ‘flexbooks’ for free on their website and they are partnered with some big names in education and technology.  While these books aren’t currently being used in very many schools, they are being successfully implemented in a handful of cases.

I chose to analyze the CK-12 Biology Textbook, designed for grades 9 and 10.  Where appropriate, I was also analyzing the CK-12 Biology Textbook-Teacher’s Edition.  As I will discuss more at the end of my discussion, both books were needed in order to complete a full review.  I also looked at the CK-12 Biology Workbook.  For all three books, I downloaded the files in PDF format for ease of use on my desktop computer (I wanted to be able to review while typing.)  They are also available, however, in mobi and epub formats for use on kindle, iPad, and android devices.

I used the website random.org to generate three random pages to assess readability and analyzed the first full paragraph of each page, numbers 676, 249, and 280.  (The pages selected are not truly random as three pages had to be discarded due to inappropriate text for analysis such as bulleted sections, images, or reference lists.)  The sample text includes four sections instead of three as the selection from page 676 did not include a 100 word sample and was expanded to include a second selection on page 677.  I used Free Fry Graph Test to analyze my text selection, listed below:

Assume that some members of a species become geographically separated from the rest of the species. If they remain separated long enough, they may evolve genetic differences. If the differences prevent them from interbreeding with members of the original species, they have evolved into a new species. Speciation that occurs in this way is called allopatric speciation.


Evolution occurs in response to a change in the environment. Environmental change often involves other species of organisms. In fact, species in symbiotic relationships tend to evolve together. This is called coevolution. As one species changes, the other species must also change in order to adapt.


The axon of many neurons has an outer layer called a myelin sheath (see Figure 22.2). Myelin is a lipid produced by a type of a glial cell known as a Schwann cell. The myelin sheath acts like a layer of insulation, similar to the plastic that encases an electrical cord. Regularly spaced nodes, or gaps, in the myelin sheath allow nerve impulses to skip along the axon very rapidly. Nerve impulses are electrical in nature. They result from a difference in electrical charge across the plasma membrane of a neuron. How does this difference in electrical charge come about? The answer involves ions, which are electrically charged atoms or molecules.


The Grand Canyon, shown here, is an American icon and one of the wonders of the natural world. It’s also a record of the past. Look at the rock layers in the picture. If you were to walk down a trail to the bottom of the canyon, with each step down you would be taking a step back in time. That’s because lower layers of rock represent the more distant past. The rock layers and the fossils they contain show the history of Earth and its organisms over a 2-billion-year time span. Although Charles Darwin never visited the Grand Canyon, he saw rock layers and fossils in other parts of the world. They were one inspiration for his theory of evolution. Darwin’s theory rocked the scientific world. In this chapter, you will read why.

Each 100 word section included approximately 8 sentences and approximately 157 syllables for readability in the 9th grade level.  Below is an image of the graph that was generated:

Out of curiosity, I also ran the sample text selection through the other readability calculators available on readabilityformulas.com which concluded that the text is at approximately an 8th grade reading or standard/average level.

Overall, the readability formulas show that the book seems to be written on a readability level at or below grade level for the published grade levels, 9th and 10th grades.  I found this to be very encouraging, especially for a science textbook that still manages to fit in concepts appropriate to learning biology on a 9th and 10th grade level.

Please see the image below for my answers to the Readability Checklist from pages 118 and 119 of the textbook. Please note that because I chose to convert scans of the checklist into a PDF form I chose to replace the check-mark response with ‘yes’ where appropriate.  (Original PDF form can be found here: Textbook Readability Checklist)


Overall, I found the textbook to be a remarkable resource and I was able to mark all of the checklist responses with either a ‘yes’ or a ‘to some extent’ answer.  Moreover, I found that the CK-12 Biology textbook was perhaps the best textbook I have ever encountered, from K-12 through Graduate school.  I will follow up my opinion by discussing the strengths and weaknesses of the book, both as a textbook generally and as a digital text specifically.

Positive Features

1. The most positive feature of the book, to me, was the presentation of information in small chunks with numerous pictures and diagrams.  I believe that for students and adults as well, information is more manageable when it is parceled into individual sections of knowledge.  Each small section of the text book focuses on one idea or concept and is often accompanied by a related graph, diagram, or relevant image.  The sections, as well as focusing on single concepts, are also short, as well as being appropriate to grade level.  When I was working on the Fry test I noticed that many sections of text were less than 100 words and that a number of texts were presented in bullet-point format rather than in traditional paragraph format.  These formatting decisions not only allow for more ease of understanding and the ability to stop and start reading without becoming lost, they also allow for students to look back and easily reference material that they did not understand.  Rather than searching through a chapter for the information on exothermic reactions, for example, they can refer directly to the section titled “exothermic reactions.”

2. Probably my second favorite feature of the book was the choice to include vocabulary words, with definitions, as the initial focus of each chapter subsection.  In the chapter subsection organization, the vocabulary word list is preceded only by the section on lesson objectives.  For example, in the subsection “Matter and Organic Compounds,” vocabulary words such as amino acid, organic compound, and double helix are clearly defined at the outset and then re-defined in-text in the remainder of the section.  This can be helpful for many reasons.  It is a useful way for students to test their vocabulary knowledge before reading the chapter, finding out what words they are familiar and unfamiliar with, it acts as a handy quick reference when studying vocabulary, and it allows students to prioritize their learning needs.  Because the vocabulary is defined in more detail in the chapter itself, students can use the vocabulary list to find otu what parts of the chapter they should be focusing on based on what vocabular terms are familiar or unfamiliar.

3. My last favorite feature of the book, though it is hard to call it the least of  three, is largely in reference to the Teacher’s Edition.  I greatly appreciated the detailed suggestions for lesson planning and for additional information that were made available in the Teacher’s Edition, and in some cases in the Student Edition as well.  For each chapter subsection, the Teacher’s Edition includes suggestions for differentiated instruction, enrichment opportunities for students who are more advanced, inquiry opportunities, and “overcoming misconceptions.”  Also included are a variety of links to outside resources including an “online resources” list at the beginning of every chapter.  The Student Edition of the textbook also includes links to outside sources and a variety of embedded links to youtube videos in addition to the pictures, graphs, and diagrams.

Positive Features: As Digital Text

1. Building on the youtube videos mentioned in the previous section, the textbook allows for students to click through to a variety of videos and outside links that will help either enhance their knowledge, clarify certain ideas and concepts, or provide additional information.  The ability to do this in-text without having to type in addresses greatly increases the likelihood of students being able to take advantage of digital extras, especially important for videos which can greatly enhance knowledge and clarify understanding.

2. The concept created by CK-12 is that of the flexbook.  While the text I chose to analyse is one of their published books, teachers are able to create their own books from provided materials and are also able to upload and include their own resources and information within the flexbooks.  This allows for the opportunity of a textbook that can be unique for every teacher and for every class year based on student needs, interests, and other factors.  I haven’t spent a lot of time investigating the flexbook concept, but I am quite intrigued and am scheduled to attend a CK-12 webinar to learn more.  The webinars are free to attend and I’d encourage anyone who was interested to check it out.  I hope to add a follow-up post after attending to share my thoughts.

3. Generally speaking, textbooks are expensive, often prohibitively so.  Many schools are using outdated textbooks and may not even have enough textbooks to go around.  Textbooks cost a considerable amount to update and to replace and digital textbooks, particularly the open source flexbooks created by CK-12, offer cost savings as well as a more environmentally friendly option.  Also, digital textbooks are more easily updated, allowing for up-to-date information to be added often without any additional cost.

Negative Features

Before I begin my three points, I must admit that I didn’t feel that there were any strong negatives to the CK-12 biology textbook, either generally or more specifically as a digital text.  The criticisms that I offer are rather mild and are quite minor when compared to the positive features the book provides.

1. The Teacher’s Edition does not include the details that are provided in the Student Edition.  While the TE does provide the outline for each section of the Student text, it does not provide the actual text that the students are reading.  The teacher is forced to ‘flip back and forth’ to see both the teacher and the student materials and cannot see the TE materials side by side with the Student text.

2.  Although I was unable to read the entire textbook, there seems to be some lack of focus on real-world rather than science-world resources.  Additional resources that provided more real-life relevant examples and exercises would be a useful addition, especially for urban, low SES, and disadvantaged youth.

3. The textbook lacks additional resources for students who are significantly below grade level either in terms of content or reading knowledge.  While this is a general complaint, I believe that it is only fair to point out that with so many text books written above grade level, this is a negative only in the most objective sense and only when viewing the CK-12 textbook singly and not when viewing it alongside similar Biology textbooks for the same grade level.

Negative Features: As Digital Text

1. The most notable negative feature of the CK-12 textbooks is the fact that they require 1:1 device availability for optimal success.  Digital texts are most useful and most relevant when every student has access to them on their own device both at school and at home.  Without 1:1 device availability, and also without home internet connection, the digital text becomes less tenable as a textbook option and the positive features that are mentioned become significantly less relevant in a situation where 1:1 and home internet access for all students are not available.

2. Another minor complaint, but all of the CK-12 books offered do not yet include Teacher’s Editions.  The Teacher’s Edition is a remarkably helpful resource and the loss of that resource is significant for books where the TE has not yet been created.  (Also, CK-12 books are not yet available for all subjects, but focus most specifically on STEM content, notably science and math.)  I want to stress, however, that this is a minor complaint, especially given that CK-12 is a non-profit and all of their resources are available free of charge.

3.  The workbooks seem to be largely concerned with the traditional mode of “busywork.”  This is EXCEEDINGLY minor, especially given the fact that there are workbooks available at all, and given that much of the content in the workbooks is both relevant and useful for all students.  (Really, I just felt compelled to have 3 things, and being that I’m not a fan of “busywork” worksheets, I thought that this was an easy choice to pick as a negative example.  A bit like picking on a sundae for having store-bought rather than home-made hot fudge sauce, though, if that makes any sense.) 

Concluding Thoughts

I was very pleasantly surprised to find the CK-12 textbooks and I would certainly be interested in using them in my future science class.  It is also perhaps worth stating the obvious, that the CK-12 resources can be printed from their PDF formats and used like traditional printed textbooks, which might be a potential option where an educator wanted to use the content provided by the CK-12 books but did not have the 1:1 device availability for his or her students.  Even as a printed rather than a digital text, the CK-12 books offer content that is grade level appropriate and appropriately formatted for ease of understanding and reference.  I’m glad to have ‘discovered’ CK-12 and I am also eager to search out other digital texts, especially options for open-source text that is not being printed for-profit by commercial textbook companies.

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