This document is intended as a resource guide for teachers to use in helping students to understand how the United States system of government operates. It examines the background, historical application, and current debate concerning the principle of checks and balances. Ten study sheets feature various figures and episodes prominently associated with the origins, development, and operation of the system. The study sheets provide the following features: background material; questions to test student knowledge; and answers to the questions. The topics include: (1) the 17th century English political philosopher John Lock; (2) the 18th century French political theorist Charles Louis Montesquieu; (3) State Governments (1776-1787); (4) "The Constitutional Convention (1787); (5) The Federalist Papers; (6) Marbury v. Madison (1803); (7) Andrew Jackson and the U.S. Bank Veto (1832); (8) Ronald Reagan--The Iran Contra Affair (1986-1987); (9) Reagan-Iran--Contra Affair (1986-1987), Editorial; and (10) Reagan--Iran Contra Affair 1986-1987), Public Opinion. In addition, nine historical examples, ranging from the assumption of war powers by Abraham Lincoln, through Franklin D. Roosevelt's "court packing" proposal, to Richard Nixon and the Watergate affair, are included for discussion. A list of references, a word search puzzle, and a crossword puzzle that tests for knowledge of constitutional checks and balances conclude the document. (DB)