Brilliant | Math and science done right
Challenge top students with adaptive math and physics problems
ACT Math Content Inventory | Virtual Nerd
Teachers looking to build a "flipped classroom" (using technology to allow kids to learn at home, then come to class for interactive work) will love that clear tutorials are already created. Students can watch the straightforward instruction and take notes at home, saving class time to focus on applying the concepts and working on cooperative projects
A useful tool for learning because it immediately lets kids see their score, what they got wrong, and the correct answer. It also makes it easy for teachers to give kids another chance and provide a new version of an assessment. All they have to do is press Regenerate, and an entirely new test appears that addresses the exact same concepts. That Quiz can be very helpful for differentiation, remediation, and providing alternative forms of an assessment.
Untangle robust math problems for all ages with plenty of teaching support. It's an excellent classroom companion that can be implemented quickly with little adjustment and a high probability of success.
CK-12 Foundation Free Online Textbooks, Math & Science Lesson Plans, Worksheets, Real World Examples
The CK-12 site has a wealth of great STEM content that teachers can work into the classroom. You're likely to find a lesson that directly corresponds to what you're teaching, and the diagrams and videos are very accessible. You can easily add content to your Google Classroom.