IXL Learning

 https://www.ixl.com/company/careers

Scroll down and look for "remote" as location. Worldwide countries, so look at job title to see which country fits.

Example posting:

 Math Curriculum Designer, Takeoff
Remote

IXL Learning, developer of personalized learning products used by millions of people globally, is seeking an experienced, passionate educator to join our team as a Math Curriculum Designer. In this role, you'll help craft exceptional educational experiences for Takeoff, IXL's breakthrough new core curriculum. You'll lend your specialized knowledge and expertise in K–12 math education to help the curriculum design team create engaging, interactive math lessons for elementary and early secondary students. Your strong writing skills, creative problem solving, educational insights, and commitment to quality will make personalized learning a reality for millions of students. 

This is a full-time remote position for candidates located in the United States. 
WHAT YOU’LL BE DOING

    Design creative, engaging, interactive math lessons both online and in print
    Write rigorous and mathematically correct content
    Consult with other curriculum designers to ensure content is age-appropriate and meets educational objectives
    Collaborate with visual designers, curriculum managers, and company leaders to determine appropriate instructional approaches
    Research and apply content requirements across many states
    Develop and manage project plans to create and deliver high-quality math content
    Ensure all project milestones are achieved within set deadlines

WHAT WE’RE LOOKING FOR 

    Bachelor's degree in a math or education-related field required - advanced degree preferred
    K–12 math teaching experience - experience as math coach or math supervisor preferred
    Excellent writing ability
    Experience in curriculum development and instructional design
    Can-do attitude with an openness to others' ideas
    Highly self-motivated and efficient with superb attention to detail