National Council of Teachers of Mathematics
The Math Forum: Divisibility Test Game "Nullo"
The lesson plan for two to four players engaged in an active card game to determine the divisibility of a number. The materials needed, the rules of the game, and the methods of scoring are all explained for the teacher.
National Council of Teachers of Mathematics
The Math Forum: Basic Divisibility Rules
This site offers a short quick reference list of divisibility rules with links to the explanations
The Math League
The Math League: Whole Numbers & Basic Properties
Here is a nice resource for students and teachers about whole numbers and their basic properties. It provides links to information on place value, expanded form, and rounding numbers are just a few of the topics on this page.
San Diego State University
San Diego State University: Divisibility War
This site offers the rules of divisibility and a game for practicing those rules. Everything is included in the site for making this game. Don't be discouraged by the length of the explanations!
Other
Project Happy Child: 100s Board Worksheets
Use these 100s Boards to have students check for divisibility by 2-12 and for square and prime numbers. Just find the links below the 100s board that has the directions printed right on top of the worksheet.