Ask a student to come up to the board and draw the body of a spider. Explain that it has a head and a thorax. Ask another student to come up and draw the body of an insect. Explain that it has a head, thorax and abdomen. Guide the students in drawing the bodies.
Ask another set of students to come up to the board. Ask the class how many legs a spider has. When someone says eight, ask the student to add eight legs. Do the same with the remaining students and insects.
List the basic differences between spiders and insects under each drawing. The differences include the following: Spiders have simple eyes, can spin silk thread, and can't fly. Insects have compound eyes, can't usually spin a thread and can sometimes fly. Spiders have piercing mouth parts, while insect mouths are more adapted for chewing.
Split the kids into groups of five, and give a numbered insect or spider model to each one. Ask them to decide whether it's an insect or spider and write it on a worksheet. Switch models until each group has seen every model.
Hold up a model and ask students to identify it. Write the answer on the board.
Hand out fact sheets about interesting local insects or spiders. Use common ones to start, like a wolf spider, a ladybug and a bee. Ask students to research one insect or one spider -- give each a simple assigned creature. Have them report to class several days later, showing a picture and explaining basic information about the assigned insect or spider.