The following resources are available in the Teacher Store.
Read-Aloud Plays: Explorers by Jeannette Sanderson.
This is a good book for learning about Leif Eriksson, Christopher Columbus, Cabeza de Vaca, Hernando de Soto, and Sieur de La Salle, and other explorers of the New World. The play format makes it an interesting and different way to learn about individual explorers. It's a "natural" for those students who enjoy drama and performance. The background information after each play is helpful for the teacher and the "Making Connections" section gives many suggestions for higher-level thinking skills and activities to go with the plays.
Hands On History Grades 4-8 Explorers by Michael Gravois.
This is a great teacher resource with many excellent projects to help your students learn about the explorers. There are many vocabulary projects, timelines, and ways to get your students involved with their explorers. One of my favorite projects is "Smells of the New World," a real multi-sensory approach to history learning. Many of these activities would supplement this month's lesson very well!
Additional books you may find in your school library:
Christopher Columbus: A STEP into Reading Step 2 book by Stephen Krensky
This is a very simple book that could be used as an explorer biography for your lower level readers.
Bartholomew and the Ooblick by Dr. Seuss.
A great literature tie-in to the "goo-ey" science lesson, this book tells what happens when an unknown substance falls from the sky in the Kingdom of Didd. Told with Dr. Seuss' usual humor, this non-rhyming book explores the limits of power and taking responsibility.
Rain Forest — Extended Thematic Unit #674, Intermediate by Teacher Created Materials, Inc.