Mathematics

Illuminations
Essential resource that contains activities, lessons, standards and web links for the classroom. Developed by the National Council of Teachers of Mathematics (NCTM).

Desmos: Powerful online graphing calculator. Graph functions, plot data, evaluate equations, explore transformations. Free. Works on any device. Classroom activities.

PEMDAS: Please Excuse My Dear Aunt Sally - The order of operations clearly explained

Great Math Resources for Teachers and Learners

YouCubed - a growth mindset approach to math
Jo Boaler of Stanford Graduate School of Education explores a rich pallette of math tools and tasks to develop understanding and mastery.
Illuminations
Essential resource that contains activities, lessons, standards and web links for the classroom. Developed by the National Council of Teachers of Mathematics (NCTM).
Math is Fun
Learning math at any level can be fun
Math Warehouse
All levels including algebra, geometry and trig. Great interactives.
Basic Mathematics
Does include some ads for paid services, but many good free tools.
Math Playground
Some ads. Easy to search. Great online manipulatives.
Cool Math
While away the hours and learn as well.

Math Apps and Platforms

Desmos graphing calculator	Freckle by Renaissance
Dreambox Learning	MobyMax

Cross-Curricular Resources

Common Sense Media
Common Sense Media focuses on what it means to be a smart, digital citizen in the 21st century. It provides reviews for games, apps and movies as well as instructional content for educators, parents and students.
WestEd
Once a regional educational lab under the Federal government, it provides excellent resources for research about teaching and learning.