This document provides a teacher's guide for a mathematics activity called "cross-NUMBERS" for young learners. The activity aims to enhance students' skills in addition and subtraction within 1000 by having them solve 10 challenging math problems and fill in the boxes of a crossword-style worksheet. The guide outlines preparing students by explaining the activity, distributing worksheets, and showing an example. Students then work individually or in groups to solve the problems while the teacher monitors and discusses answers.