With more than 140 countries currently offering or in transition to a kindergarten through grade 12 (K–12) school education system, this desk study explored the experiences of four countries---Mongolia, Philippines, Poland, and Turkey---and one Canadian province, Ontario, in preparing and implementing K–12 systems. Lessons learned from the five diverse jurisdictions are: (i) align the education system with macro policies, (ii) view transition to K–12 as part of a package of reforms, (iii) prioritize improving student learning, (iv) consider teacher development as critical, (v) avoid high-stakes examinations, and (vi) focus on higher order curriculum and assessments.