This short video and interactive assessment activity is designed to give fourth graders an overview of the sum of the angles of a triangle.

CK-12 Foundation's Trigonometry FlexBook is an introduction to trigonometry for the high school student. It includes chapters on graphs of trigonometric functions, trigonometric identities, inverse trigonometric functions, triangles and vectors, and the polar system.

CK-12 Foundation's Trigonometry FlexBook is an introduction to trigonometry for the high school student. Topics include: Trigonometric Identities & Equations, Circular Functions, and Polar Equations & Complex Numbers.

CK-12's Texas Instruments Trigonometry Student Edition Flexbook is a helpful companion to a trigonometry course, providing students with more ways to understand basic trigonometric concepts through supplementary exercises and explanations.

CK-12's Texas Instruments Trigonometry Teacher's Edition Flexbook is a helpful companion to a trigonometry course, providing students with more ways to understand basic trigonometric concepts through supplementary exercises and explanations.

CK-12 Trigonometry Teacher's Edition provides tips and common errors for teaching CK-12 Trigonometry Student Edition. The solution and assessment guides are available upon request.

This short video and interactive assessment activity is designed to teach fifth graders about turning numbers into words within word problems.

This short video and interactive assessment activity is designed to teach third graders about turning words into numbers using place value models.

This short video and interactive assessment activity is designed to give fourth graders an overview of metric capacity operations.

From CK-12, U.S. History Sourcebook - Advanced covers U.S. history from Colonial America through World War I. This book provides high school U.S. History teachers and students with sets of primary and secondary sources about important topics. Some teachers will use it as a supplement to a traditional textbook. For those looking to leave the textbook behind entirely, it will provide a course with basic structure and continuity, and will reduce the burden of finding new primary sources for each class meeting. However, it is not yet comprehensive enough to meet the coverage requirements of, for example, an Advanced Placement test.

From CK-12, U.S. History Sourcebook - Basic covers U.S. history from Colonial America through World War I. This book provides high school U.S. History teachers and students with sets of primary and secondary sources about important topics. Some teachers will use it as a supplement to a traditional textbook. For those looking to leave the textbook behind entirely, it will provide a course with basic structure and continuity, and will reduce the burden of finding new primary sources for each class meeting. However, it is not yet comprehensive enough to meet the coverage requirements of, for example, an Advanced Placement test.

Understanding Biodiversity presents an overview of biodiversity, its importance and relevance to humans, all living things, and the Earth. It includes species pages and a template to engage and involve students in real-life data collection.

This short video and interactive assessment activity is designed to teach fourth graders how to, given the perimeter, find the side length and area - squares.

This short video and interactive assessment activity is designed to teach third graders about given the perimeter, find the side length and area - squares.

This short video and interactive assessment activity is designed to teach fifth graders about using the four operations with money - word problems.

This short video and interactive assessment activity is designed to teach fourth graders about using the four operations with money - word problems.

This short video and interactive assessment activity is designed to teach third graders about understanding division with remainders and illustrations.

This short video and interactive assessment activity is designed to teach fourth graders about place value problems involving money.

This short video and interactive assessment activity is designed to teach fifth graders about multiplication and division with money.

This short video and interactive assessment activity is designed to teach second graders about using timelines to 1-minute increments.