National Council of Teachers of Mathematics has much to offer for both students and mathematics teachers. Teachers can use this website to access the NCTM standards. It also offers various opportunities for professional development.
Engage NY is a great tool for teachers, students, and families to use. This website is mainly utilized to access the common core curriculum for ELA, Mathematics, and Social Studies. The modules also located here are used for the teachers to refer to, to assure that they are sticking to the curriculum and covering all topics necessary in order for their students to be successful in the following years.
Khan academy is a good resource for both students and teachers. It is a great tool for students to review previously learned material. Teachers can also incorporate a clip on this website into their lesson to provide examples and an explanation of the material to their class.