If you're not yet aware of youcubed from Stanford University, now just might be the time to check it out. Led by Jo Boaler and Cathy Williams, the center's goal is to, "inspire, educate and empower teachers of mathematics, transforming the latest research on math learning into accessible and practical forms". The website hosts lessons, research, mathematical tasks, short videos, and professional development all designed to help math teachers and students rethink about and engage in mathematics.
An excellent way to get started using youcubed's resources is with The Week of iMath. Designed to support a growth mindset and inspire learning of mathematics, the set of lessons are great way to start math lessons early in the school year. Each of the five lessons are accessible for grades 3 through high school and are available free through the youcubed website here. Happy learning!