This book is a revised edition of one of the products of a project, "Teaching Mathematics and Science Concepts, K-6, funded by the New York State Education Department. The project was a collaborative effort by mathematics and science education faculty at the State University of New York at Albany and representatives of eight school districts in the Greater Capital District area of New York State. This book contains lesson ideas that reflect the belief that science and mathematics are opposite sides of the same coin. The lessons incorporate concepts and processes from both subjects. Activities were chosen for this booklet if they met the following criteria: (1) they combined important mathematics and science in a single lesson; (2) had been tried out by classroom teachers and elementary school children; (3) involved "hands-on" activities; (4) used readily available, everyday materials; and (5) could be used as the basis for further activities. Each activity includes the procedure, needed materials, key concepts, skills and processes, background information, and extensions. Included is a list of free and inexpensive materials that have proved useful in teaching science and mathematics and contains everything needed for the activities in this booklet and more. The topics of geometry, shapes, the earth, measuring, counting, inclined planes, work, gravity, friction, observing, classifying, angles, dew point, probability, symmetry, variation in nature, metric system, data collecting, estimation, ratios, proportion, melting, freezing, graphs, inferring, patterns, feeding and locomotion of animals, adaptations in animals, volume, ground water, and water supply are presented. A section "Sources of Further Ideas" contains a brief list of professional journals, teacher idea/reference books, curriculum projects along with a list of useable junk. (KR)