A+Math from Varsity Tutors  Free worksheets, flashcards, math games and homework helper. 

Corbettmaths Primary and Corbettmaths Developed in the UK, both Corbettsmaths Primary and Corbettsmath have great videos, study cards, work sheets and practice papers. These are good resources, but you will have to look for what you need: everything is keyed to British standards, not the Common Core. All of the videos are available on their YouTube Channel  

Edhelper  Free distance learning resources: printables and online practice. Teaching ideas.

Illuminations from the National Council of Teachers of Mathematics. Free lesson plans, interactives, mobile games, and brain teasers for all grade levels aligned to NCTM and Common Core standards. E-examples of problems and web-sketchpad optimized for tablets and computers. Good resource for virtual teaching.

Illustrative Mathematics Free resources for teachers include illustrative tasks organized by content and practice standards, several blogs, one of which focuses on distance learning and English learners.

Khan Academy and Khan Academy Kids If you are not already familiar with these two resources, there may be no hope left. My son taught himself college calculus using Khan Academy!

MathSnacks Animations, games, and interactive tools developed by New Mexico State Univeristy to help middle school students learn math concepts. An Ios app is available for download. Content is available in Spanish. MathSnacks also has a YouTube Channel. The use of MathSnacks is supported by research as improving students math ability.

Prodigy Math Teachers and parents can create free accounts to use the Prodigy Math Game to help their students get extra practice in math. The game aligns with Georgia standards and is supported by research demonstrating its efficacy. A great resource for virtual learning, grades 1-8.

SplashLearn Parents and teachers can create free accounts at this award winning website for math learning grades K-5. Students receive a personalized learning path for catching up, enrichment, or practice; interactive games and rewards motivate students to learn.  The free SplashLearn Math app is available for ipads and iphones.

Woot Math  From the Woot Math website: "Woot Math's free tier for teachers provides hours of in-classroom use so that you can meaningfully try Adaptive Practice with your students. In addition to providing access to core, foundation topics supporting mastery of fractions, you can choose two additional topics that directly meet your instructional goals."  Grades 6-8.

Woot Math: Making Students' Thinking Visible from Woot Math on Vimeo.