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CK-12 FlexBook 2.0

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Spec score 8.9 #1 of 29 in K-12 Curriculum Platforms

What it is

CK-12 FlexBook 2.0 provides customizable digital textbooks for K–12 subjects including science, math, and social studies. Lessons can combine text with PLIX interactives, simulations, adaptive practice, and related learning materials. Adaptive Practice draws questions from a library of more than 150,000 and adjusts selections based on student answers. Teachers can assign lessons, videos, interactives, and practice to whole classes or differentiated groups, then view progress reports. Educators can reorder chapters and edit or add content in customized FlexBooks. The service works in browsers on laptops, desktops, Chromebooks, tablets, and mobile devices, and is listed at free. Standalone Simulations and PLIX Interactives require a tablet-size screen or larger. Users may download PDFs of FlexBooks they create or customize, though interactive content may not render; CK-12-created PDFs are not downloadable. CK-12 says it is still converting all core content to FlexBook 2.0. Listed SSO or LMS partners include Google Classroom, Canvas, Schoology, Kiddom, Clever, and ClassLink.

Spec sheet

What it does
FlexBook 2.0 is CK-12’s interactive digital textbook platform for math and science lessons with embedded learning resources.Read 15 Oct 2026 · help.ck12.org
Purpose
FlexBooks are customizable digital textbooks for K–12 subjects including science, math, and social studies.Read 7 Oct 2026 · help.ck12.org
Audience
FlexBooks are designed for educators and students and cover K–12 topics.Read 7 Oct 2026 · help.ck12.org
Integrations
CK-12 lists Google Classroom, Canvas, Schoology, Kiddom, Clever and ClassLink as SSO or LMS partners.Read 15 Oct 2026 · info.ck12.org
Security
CK-12 says it uses administrative, technological and physical safeguards and encrypts transmissions with SSL or similar technology, while disclaiming a guarantee of security.Read 15 Oct 2026 · help.ck12.org
Support
Users can contact CK-12 Support by starting a support ticket or sending an email.Read 7 Oct 2026 · help.ck12.org
License
Curriculum Materials use CK-12’s own license allowing copying, distribution and modification only for defined educational purposes, with attribution and license notices.Read 15 Oct 2026 · help.ck12.org
Headquarters
CK-12 lists its headquarters at 4300 Bohannon Drive, Suite 200, Menlo Park, California.Read 15 Oct 2026 · help.ck12.org
Accessibility
CK-12’s 2024 VPAT states that the FlexBooks 2.0 platform meets AA conformance across the criteria covered by the report.Read 15 Oct 2026 · static.ck12.org
Adaptive practice
Each FlexBook lesson can provide adaptive practice with standards-aligned questions, hints and step-by-step solutions.Read 15 Oct 2026 · info.ck12.org
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.Read 7 Oct 2026 · help.ck12.org
Bulk assignment
Teachers can assign multiple concepts to students in one operation.Read 15 Oct 2026 · help.ck12.org
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.Read 15 Oct 2026 · help.ck12.org
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.Read 15 Oct 2026 · help.ck12.org
Company founded
LinkedIn lists CK-12 Foundation’s founding year as 2007.Read 15 Oct 2026 · linkedin.com
Company type
LinkedIn identifies CK-12 Foundation as a nonprofit in primary and secondary education with 51–200 employees.Read 15 Oct 2026 · linkedin.com
Customization
Teachers can customize and create FlexBooks, chapters and sections and add existing CK-12 content.Read 15 Oct 2026 · help.ck12.org
Device access
CK-12 says FlexBooks are usable on smartphones, Chromebooks, tablets, laptops and desktops.Read 15 Oct 2026 · info.ck12.org
Funding
CK-12 says it is a 501(c)(3) funded through donations, grants and philanthropic support.Read 15 Oct 2026 · help.ck12.org
Google Classroom limitation
Google Classroom co-teachers cannot view CK-12 assignment reports through CK-12’s co-teacher functionality.Read 15 Oct 2026 · help.ck12.org
Integrated modalities
The platform places PLIX activities, simulations, adaptive practice and related modalities inside lessons.Read 15 Oct 2026 · help.ck12.org
Lesson content
FlexBook 2.0 lessons combine text, PLIX interactives, simulations, adaptive practice, and related learning materials.Read 7 Oct 2026 · help.ck12.org
Lesson format
Lessons combine reading with embedded videos, interactives and practice while keeping the table of contents and toolbar on the same page.Read 15 Oct 2026 · help.ck12.org
Limit: AI image handling
Apple App Store reviewers said Flexi sometimes fails to interpret worksheet images accurately, despite otherwise useful explanations and study tools.Read 15 Oct 2026 · apps.apple.com
Limit: navigation and setup
Teacher reviewers reported clunky navigation, cumbersome class setup and difficulty finding or using class codes.Read 15 Oct 2026 · commonsense.org
Limit: quiz quality
Common Sense’s kid-review summary reports confusing or disconnected quizzes, inconsistent marking and insufficient explanations.Read 15 Oct 2026 · commonsensemedia.org
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.Read 15 Oct 2026 · sikayetvar.com
LMS roster sync
For Canvas, Schoology and Google Classroom classes, enrollment is managed in the LMS and synchronized into CK-12.Read 15 Oct 2026 · help.ck12.org
LTI support
The administrator help center documents an LTI 1.3 installation for Canvas.Read 15 Oct 2026 · help.ck12.org
Notable update
Flexi iOS version 1.0.12, listed September 28, added a dark theme plus bug fixes and performance improvements.Read 15 Oct 2026 · apps.apple.com
Offline and PDF
Users can download PDFs of FlexBooks they create or customize, but interactive content may not render and CK-12-created PDFs are not downloadable.Read 7 Oct 2026 · help.ck12.org
Praise: content breadth
Common Sense reviewers describe CK-12 as well organized, accessible STEM content with multimedia resources, free access and availability in nearly 50 languages.Read 15 Oct 2026 · commonsensemedia.org
Praise: engagement
An EducationWorld review praised the large free library of text, video, audio, quizzes and interactive materials and the ability to edit FlexBook texts.Read 15 Oct 2026 · educationworld.com
Praise: personalization
A Common Sense Education teacher reviewer said CK-12 supported independent exploration and deeper-thinking questions that increased student engagement when combined with other media.Read 15 Oct 2026 · commonsense.org
Privacy and security
CK-12 says it uses administrative, technological, and physical safeguards and encrypts information transmissions using SSL or similar technologies.Read 7 Oct 2026 · help.ck12.org
Public API or SDK
The public administrator and developer-facing documentation reviewed describes LMS and LTI integrations but does not publish a general-purpose CK-12 API or SDK.Read 15 Oct 2026 · help.ck12.org
Rating on Apple App Store
4.3 out of 5 from 14 ratings for Flexi AI Tutor & Homework Help.Read 15 Oct 2026 · apps.apple.com
Rating on Chrome Web Store
4.9 out of 5 from 12 ratings for the Flexi AI Tutor extension.Read 15 Oct 2026 · chromewebstore.google.com
Rating on Google Play
4.0 out of 5 from 4.1K reviews for the Flexi AI Tutor app.Read 15 Oct 2026 · play.google.com
Rating on Knoji
4.1 out of 5 from 46 ratings for CK-12.Read 15 Oct 2026 · ck12.knoji.com
Self-hosting
CK-12’s privacy policy says the platform is operated and hosted on servers in the United States, with no self-hosting procedure documented.Read 15 Oct 2026 · help.ck12.org
Student data
CK-12 says it does not sell student information or use or disclose it for behavioral advertising to students.Read 7 Oct 2026 · help.ck12.org
Student practice
Adaptive Practice selects questions from CK-12’s library of more than 150,000 questions and adjusts them based on student answers.Read 7 Oct 2026 · int-www.ck12.org
Support documentation
The Help Center contains role-specific student, teacher, parent and administrator sections plus guides for assignments, customization, accessibility, privacy and integrations.Read 15 Oct 2026 · info.ck12.org
Teacher analytics
CK-12 lists teacher Insights for monitoring student performance.Read 15 Oct 2026 · info.ck12.org
Teacher tools
Teachers can assign lessons, interactives, videos, and adaptive practice to a class or differentiated groups and view student progress reports.Read 7 Oct 2026 · help.ck12.org

Plans and prices

CK-12 FlexBook 2.0 Free No charge Free access for students, teachers, schools and districts · online FlexBooks, interactive lessons, practice and teacher tools Read 15 Oct 2026 · info.ck12.org
FlexBook 2.0 Free Free online customizable digital textbook; content varies by subject and book Read 7 Oct 2026 · help.ck12.org

Every CK-12 FlexBook 2.0 plan and price →

Strong points and limits

Strong points

  • Free customizable digital textbooks.
  • Adaptive Practice uses a library of over 150,000 questions.
  • Teachers can view student progress reports.
  • Works in browsers across computers, tablets, and mobile devices.

Limits

  • Standalone Simulations and PLIX require tablet-size screens or larger.
  • Interactive content may not render in downloaded PDFs.
  • CK-12-created PDFs are not downloadable.
  • Not all core content has been converted.

Who it suits

FlexBook 2.0 suits K–12 educators and students who want customizable digital textbooks with lessons, practice, and interactive materials. Teachers can assign work to classes or differentiated groups and review progress reports.

Verdict

FlexBook 2.0 combines editable textbooks with assignments, adaptive practice, and classroom reporting at no listed cost. Check subject and book availability, and note the limits on standalone interactives and PDF downloads.

Where Specifiction places it

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