This document provides guidance for teachers on preparing their classroom in the first 20 days of school. It outlines a 3 stage process: 1) Planning - considering classroom layout, supplies, routines. 2) Foundation - establishing routines, teaching expectations, providing feedback. 3) Maintenance - continuing to review routines, reflect on successes and challenges, and provide consistent positive feedback. Specific tips are given for each stage, such as drawing a classroom layout, common routines to establish, and ways to recognize students. The overall message is the importance of spending the first few weeks planning carefully, explicitly teaching routines and expectations, and maintaining positive reinforcement.