This document is a collection of activity-based mathematics lessons for grades K-4 from the "Ideas" department in "Arithmetic Teacher: Mathematics Education through the Middle Grades." Each lesson includes background information, objectives, directions, extensions, and student worksheets. A matrix is included which correlates the titles of the activities with the National Council of Teachers of Mathematics Standards that apply to the lessons. Lesson titles include: "Stones for the Postman's Palace,""Love Stamps,""How Mail Moves,""Beverage Sharing and Serving,""Measurement Scavenger Hunt,""What Can You Build with Two Triangles?,""How Do You Build Triangles?,""Graphing Trash Material,""Classroom Paper,""Buttons! Buttons!,""Shapes Art,""Sorting SKITTLES/Graphing SKITTLES,""Geometric Art,""Shapely Art,""Picturing Our Building,""Building with Newspaper Dowels,""Figuring in Football,""Get the Picture - Get the Story,""The Rhythm of Counting,""Measuring Music,""Which Flavor Wins the Taste Test?,""You Are the Pollster,""Exploring a Community,""Getting to Know You,""Have a Seat,""Computation Court: You Be the Judge,""Hop to It!,""Long Leaps for Olympic Gold,""Numbers on a Kite Tail,""Pin the Tail on the Kite,""How Big Is Your Heart?,""Every Beat of Your Heart,""Discovering Figures,""Geometric Figures,""Toy-Shop Numbers,""Post-Office Numbers,""Cut to Create,""Create a New Figure," Pizza Topping," and "Thumbprint Graph." (MKR) "Favorite Television Programs,""Pizza-Topping Combinations,""Favorite Pizza Toppings," and"Thumbprint Graph." (MKR)