CK-12 FlexBook 2.0
CK-12 FlexBook 2.0 provides free, customizable digital textbooks for K–12 subjects such as science, math and social studies.
What CK-12 FlexBook 2.0 is
CK-12 FlexBook 2.0 provides free, customizable digital textbooks for K–12 subjects such as science, math and social studies. Lessons can combine text with PLIX interactives, simulations, adaptive practice and related learning materials. Adaptive Practice draws from CK-12’s library of more than 150,000 questions and adjusts selections in response to student answers. Teachers can assign lessons, interactives, videos and practice to a whole class or differentiated groups, then view student progress reports. Educators can customize books by reordering chapters and adding or editing content. The service works in a browser on laptops, desktops, Chromebooks, tablets and mobile devices; standalone Simulations and PLIX Interactives require a tablet-size screen or larger. Users may download PDFs of FlexBooks they create or customize, although interactive content may not render, and CK-12-created PDFs are not downloadable. CK-12 has converted many of its most-used books to FlexBook 2.0 and is still working on the rest of its core content. Its listed partners include Google Classroom, Canvas, Schoology, Kiddom, Clever and ClassLink. FlexBook 2.0 is designed for educators and students.
Good
- Free digital textbooks cover science, math and social studies.
- Lessons can combine text, interactives, simulations and adaptive practice.
- Practice adapts questions based on student answers.
- Teachers can assign material and view progress reports.
- Educators can reorder chapters and edit book content.
Watch out
- Standalone Simulations and PLIX Interactives need a tablet-size screen or larger.
- Interactive content may not render in downloaded PDFs.
- CK-12-created PDFs are not downloadable.
- Not all core content has been converted to FlexBook 2.0.
Who it suits
FlexBook 2.0 suits K–12 educators who want to adapt textbook chapters and assign lessons or practice to classes and differentiated groups. Students can use its lessons and adaptive practice, while the browser access supports a range of device types.
Verdict
Choose FlexBook 2.0 if you want free, customizable K–12 textbooks with teacher assignments and adaptive practice. Look elsewhere if you require every core title in FlexBook 2.0 or downloadable PDFs of CK-12-created books.
Plans and prices
From CK-12 FlexBook 2.0's own pricing page, checked 15 Oct 2026.
| Plan | Price | What it gives you |
|---|---|---|
| CK-12 FlexBook 2.0 | Free | Free access for students, teachers, schools and districts · online FlexBooks, interactive lessons, practice and teacher tools · No charge |
| FlexBook 2.0 | Free | Free online customizable digital textbook; content varies by subject and book |
The facts
Each one read from CK-12 FlexBook 2.0's own pages, with the date it was checked.
What it does
- Accessibility
- CK-12’s 2024 VPAT states that the FlexBooks 2.0 platform meets AA conformance across the criteria covered by the report.checked 15 Oct 2026
- Adaptive practice
- Each FlexBook lesson can provide adaptive practice with standards-aligned questions, hints and step-by-step solutions.checked 15 Oct 2026
- Audience
- FlexBooks are designed for educators and students and cover K–12 topics.checked 7 Oct 2026
- Availability limit
- CK-12 says it has converted many of its most-used books to FlexBook 2.0 and is still working to convert all core content.checked 7 Oct 2026
- Bulk assignment
- Teachers can assign multiple concepts to students in one operation.checked 15 Oct 2026
- Children’s privacy
- For school-contract student accounts, CK-12 treats student records as controlled by and owned by the contracting school and provides parent rights to review or delete child information.checked 15 Oct 2026
- Commercial-use restriction
- The curriculum license prohibits commercial use, AI or machine-learning training, automated derivative creation and redistribution through third-party services without permission.checked 15 Oct 2026
- Customization
- Teachers can customize and create FlexBooks, chapters and sections and add existing CK-12 content.checked 15 Oct 2026
- Funding
- CK-12 says it is a 501(c)(3) funded through donations, grants and philanthropic support.checked 15 Oct 2026
- Google Classroom limitation
- Google Classroom co-teachers cannot view CK-12 assignment reports through CK-12’s co-teacher functionality.checked 15 Oct 2026
- Integrated modalities
- The platform places PLIX activities, simulations, adaptive practice and related modalities inside lessons.checked 15 Oct 2026
- Integrations
- CK-12 lists Google Classroom, Canvas, Schoology, Kiddom, Clever and ClassLink as SSO or LMS partners.checked 15 Oct 2026
- Lesson content
- FlexBook 2.0 lessons combine text, PLIX interactives, simulations, adaptive practice, and related learning materials.checked 7 Oct 2026
- Lesson format
- Lessons combine reading with embedded videos, interactives and practice while keeping the table of contents and toolbar on the same page.checked 15 Oct 2026
- License
- Curriculum Materials use CK-12’s own license allowing copying, distribution and modification only for defined educational purposes, with attribution and license notices.checked 15 Oct 2026
- Limit: AI image handling
- Apple App Store reviewers said Flexi sometimes fails to interpret worksheet images accurately, despite otherwise useful explanations and study tools.checked 15 Oct 2026
- Limit: navigation and setup
- Teacher reviewers reported clunky navigation, cumbersome class setup and difficulty finding or using class codes.checked 15 Oct 2026
- Limit: quiz quality
- Common Sense’s kid-review summary reports confusing or disconnected quizzes, inconsistent marking and insufficient explanations.checked 15 Oct 2026
- Limit: technical reliability
- A customer-complaint review page reports user complaints about pages not loading, slow performance, sign-in problems and malfunctioning assessments or assignments.checked 15 Oct 2026
- LMS roster sync
- For Canvas, Schoology and Google Classroom classes, enrollment is managed in the LMS and synchronized into CK-12.checked 15 Oct 2026
The company
- Company founded
- LinkedIn lists CK-12 Foundation’s founding year as 2007.checked 15 Oct 2026
- Company type
- LinkedIn identifies CK-12 Foundation as a nonprofit in primary and secondary education with 51–200 employees.checked 15 Oct 2026
- Headquarters
- CK-12 lists its headquarters at 4300 Bohannon Drive, Suite 200, Menlo Park, California.checked 15 Oct 2026
Where it runs
- Device access
- CK-12 says FlexBooks are usable on smartphones, Chromebooks, tablets, laptops and desktops.checked 15 Oct 2026
The full review of CK-12 FlexBook 2.0
CK-12 FlexBook 2.0 is a free, browser-based platform for customizable K–12 digital textbooks and interactive lessons. It is best suited to educators who want to reshape chapters, assign differentiated work, and monitor progress, alongside students who learn well from simulations and adaptive practice. Its main drawback is coverage: some core books are still being converted, and the strongest interactives need a larger screen.
Overview
FlexBooks cover K–12 subjects such as science, mathematics, and social studies. A lesson may combine explanatory text with PLIX interactives, simulations, adaptive practice, and related learning materials, giving teachers more ways to present and reinforce a concept than a static e-book. The exact mix depends on the subject and individual book.
Educators can reorder chapters and add or edit material in a customized FlexBook. That makes it practical for aligning a textbook with a particular sequence or class emphasis. CK-12 has converted many of its most-used titles to FlexBook 2.0 but is still working through all core content, so it may not cover every course a school needs.
Key features
Adaptive practice and assignments
Adaptive Practice selects from more than 150,000 questions and changes subsequent questions according to a student's answers. It is a stronger fit for individualized reinforcement than a fixed worksheet sequence. Teachers can assign lessons, interactives, videos, and adaptive practice to a whole class or differentiated groups, then use progress reports to see how students are doing.
Interactive instruction
Simulations and PLIX activities can turn an explanation into an activity, particularly in science. Standalone simulations and PLIX Interactives require a tablet-size screen or larger, however, so a phone-only workflow is unsuitable for those materials.
Customization and integrations
Chapter reordering and editable content support teacher-authored courses rather than forcing every class through the same textbook path. Google Classroom, Canvas, Schoology, Kiddom, Clever, and ClassLink are listed as SSO or LMS partners, which can reduce friction for schools already using those systems.
Accessibility, privacy, and offline use
Readers can change font size, background color, and line spacing. Lesson text also supports text-to-speech and Google Translate. CK-12 says it uses administrative, technological, and physical safeguards, encrypts transmissions with SSL or similar technology, and does not sell student information or use it for behavioral advertising to students.
Users may download PDFs of FlexBooks they create or customize, but interactive elements may not render in those files, and CK-12-created books cannot be downloaded as PDFs. Support is available through a ticket or email.
Pricing
| Plan | Price | Includes |
|---|---|---|
| FlexBook 2.0 | free | Free online customizable digital textbook; content varies by subject and book |
There are no paid tiers, seat charges, quotas, or renewal terms stated for this plan. The trade-off for the zero price is not a reduced feature tier but variable book coverage, no PDF downloads for CK-12-created books, and possible loss of interactive behavior in downloaded custom-book PDFs.
Platforms
CK-12 works in a browser on laptops, desktops, Chromebooks, tablets, and mobile devices, with Android and iOS access also supported. A tablet-size screen or larger is required for standalone Simulations and PLIX Interactives, making a laptop, Chromebook, or tablet the better choice for full lesson coverage.
Who it's for
FlexBook 2.0 is a strong fit for K–12 teachers and schools that want free digital texts they can rearrange and supplement, assign to classes or groups, and pair with adaptive practice. It also suits students who benefit from interactive science materials and performance-responsive questions. It is less suitable for programs that require every CK-12 core title in the newer format, depend on phone-sized screens for interactives, or need downloadable PDFs of CK-12-authored books.
Pros and cons
Pros
- Free access: the FlexBook 2.0 plan costs nothing.
- Teacher control: chapters can be reordered and content added or edited.
- Responsive practice: more than 150,000 questions are selected and adjusted based on answers.
- Differentiated assignments: teachers can target a class or separate groups and review progress reports.
- Broad delivery options: browser access spans computers, Chromebooks, tablets, and mobile devices.
- Useful accessibility controls: font, background, spacing, text-to-speech, and translation options support varied readers.
Cons
- Incomplete conversion: not all core content is yet available in FlexBook 2.0.
- Screen requirement: standalone simulations and PLIX interactives need a tablet-size display or larger.
- PDF limitations: custom-book PDFs may lose interactive content, and CK-12-created books cannot be downloaded.
Alternatives
Choose MobyMax instead if you want a freemium platform with Android, iOS, macOS, web, and Windows support and a paid Family plan at $7.99 a month.
Khan Academy is an alternative for learners seeking a freemium service with Android, iOS, and web access; its Enterprise Starter plan is $10 a year per student for U.S. schools and districts with 1,000 or fewer licenses.
Pick Amplify Classroom for free web-based K–12 math, literacy, and science lessons with a Teacher Dashboard and Polypad manipulatives.
EL Education Curriculum provides free web-based language-arts resources, with an account required for some materials.
Choose Eureka Math for free PreK–12 PDF curriculum and its broader digital-suite offering.
Illustrative Mathematics offers a full TK–12 OER curriculum online at no cost, including downloadable and printable teacher and student PDFs.
Oak National Academy is a free web and API platform with no paywalls or package tiers.
Choose OpenSciEd for free downloadable science curriculum resources, with registration required for educators or parents.
For broader browsing, see K-12 Curriculum Platforms, Open Educational Resource Platforms, Science Learning Software, and Digital Textbook Platforms.
Verdict
Choose CK-12 FlexBook 2.0 if you are a K–12 educator who wants free, editable digital textbooks with differentiated assignments, adaptive practice, and interactive lessons. Look elsewhere if your curriculum depends on a core book that has not been converted, requires phone-sized interactive access, or needs downloadable PDFs of CK-12-created books.
Getting started
- Visit https://www.ck12.org/.
- Open the service in a browser on a laptop, desktop, Chromebook, tablet or mobile device.
- Use a FlexBook 2.0 textbook, or customize one by reordering chapters and adding or editing content.
- Assign lessons, interactives, videos or adaptive practice to a class or differentiated groups.
- Download a PDF of a FlexBook you create or customize if a downloadable copy is needed.
Limits worth knowing
The free FlexBook 2.0 plan provides an online customizable textbook, with content varying by subject and book. Standalone Simulations and PLIX Interactives require a tablet-size screen or larger; PDF downloads may not preserve interactive content, and CK-12-created PDFs are not downloadable.
Questions
Is CK-12 FlexBook 2.0 free?
Yes. The listed FlexBook 2.0 plan is free and provides an online customizable digital textbook.
Which subjects and grades does it cover?
FlexBooks cover K–12 subjects including science, math and social studies.
Which devices can access it?
It works in a browser on laptops, desktops, Chromebooks, tablets and mobile devices. Standalone Simulations and PLIX Interactives need a tablet-size screen or larger.
Can teachers assign content and track students?
Teachers can assign lessons, interactives, videos and adaptive practice to a class or differentiated groups, and view student progress reports.
Can I download a PDF?
Users can download PDFs of FlexBooks they create or customize. Interactive content may not render, and CK-12-created PDFs are not downloadable.
Which LMS or SSO partners are listed?
CK-12 lists Google Classroom, Canvas, Schoology, Kiddom, Clever and ClassLink as SSO or LMS partners.
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