What do you want to learn today?

Math

Elementary Math

Grade 1
Grade 2
Grade 3
Grade 4
Grade 5

Interactive

Math 6
Math 7
Math 8
Algebra I
Geometry
Algebra II

Conventional

Math 6
Math 7
Math 8
Algebra I
Geometry
Algebra II
Probability & Statistics
Trigonometry
Math Analysis
Precalculus
Calculus

What's the difference?

Science

Grade K to 5
Earth Science
Life Science
Physical Science
Biology
Chemistry
Physics
Advanced Biology

FlexLets

Math FlexLets
Science FlexLets

English

Writing
Spelling

Social Studies

Economics
Geography
Government
History
World History
Philosophy
Sociology

More

Astronomy
Engineering
Health
Photography
Technology

College

College Algebra
College Precalculus
Linear Algebra
College Human Biology
The Universe

Adult Education

Basic Education
High School Diploma
High School Equivalency
Career Technical Ed
English as 2nd Language

Country

Bhutan
Brasil
Chile
Georgia
India

Translations

Spanish
Korean
Deutsch
Chinese
Greek
Polski

EXPLORE

Flexi
A FREE Digital Tutor for Every Student
FlexBooks 2.0
Customizable, digital textbooks in a new, interactive platform
FlexBooks
Customizable, digital textbooks
Schools
FlexBooks from schools and districts near you
Study Guides
Quick review with key information for each concept
Adaptive Practice
Building knowledge at each student’s skill level
Simulations
Interactive Physics & Chemistry Simulations
PLIX
Play. Learn. Interact. eXplore.
CCSS Math
Concepts and FlexBooks aligned to Common Core
NGSS
Concepts aligned to Next Generation Science Standards
Certified Educator
Stand out as an educator. Become CK-12 Certified.
Webinars
Live and archived sessions to learn about CK-12

Other Resources
CK-12 Resources
Concept Map
Testimonials
CK-12 Mission
Meet the Team
CK-12 Helpdesk

FlexLets

FlexLets

Know the essentials.

CRISP ACADEMY

California

Can't find your school?

CRISP ACADEMY View School

Georgia
CRISP ACADEMY

Created by: Elizabeth Salvi

Open FlexBook^®

Organisms and Ecosystems

Elizabeth Salvi

CK-12 Foundation is a non-profit organization that provides free educational materials and resources.

FLEXIAPPS

ABOUT

Our mission Meet the team Partners Press Careers Security Blog CK-12 usage map Testimonials

SUPPORT

Certified Educator Program CK-12 trainers Webinars CK-12 resources Help Contact us

BYCK-12

Common Core Math K-12 FlexBooks College FlexBooks Tools and apps

CONNECT

v2.11.14.20260422065310-40fcf4eca8

© CK-12 Foundation 2025 | FlexBook Platform®, FlexBook®, FlexLet® and FlexCard™ are registered trademarks of CK-12 Foundation.

Terms of use Privacy Attribution guide

Content is licensed under CK-12 Curriculum Materials License

Curriculum Materials License

Please wait...

To use this website, please enable javascript in your browser. Learn more

Oops, looks like cookies are disabled on your browser. Click here to see how to enable them.