National Council of Teachers of Mathematics (NCTM) offers many different grants for math teachers for grades K-12. The Connecting Mathematics to Other Subject Areas (up to $4000, November 1 deadline), Designing Innovative Lessons and Activities for Mathematics Teaching K-8 ($5000, November 1 deadline), and Enhancing Student Mathematics Learning Through the Use of Tools and Technology (up to $3000, May 1 deadline) are great grants to check out. Applicants must be members of NCTM to apply.
Issuer: Private Non-profit
Awardee: K-12 educators