Introduction to the Addition and Subtraction Milestones Back to: Introduction to Milestones for Basic Addition & Subtraction Facts Previous Lesson For session coordinators Lesson 1 within section Getting Started. You must enroll in this course to access course content. Next Lesson Part 2 Lesson 2 within section Milestones. You must enroll in this course to access course content. Previous Lesson For session coordinators Lesson 1 within section Getting Started. You must enroll in this course to access course content. Next Lesson Part 2 Lesson 2 within section Milestones. You must enroll in this course to access course content.