http://www.php.net/manual/ja/language.oop5.static.php

class_static_self_test.php

<?php

class A {
	public static $name = "ClassA";
	public static function printStatic() {
		echo static::$name.PHP_EOL;
	}
	public static function printSelf() {
		echo self::$name.PHP_EOL;
	}
}

class B extends A {
	public static $name = "ClassB";
}

class C extends A {
	public static $name = "ClassC";
	public static function printStatic() {
		echo static::$name.PHP_EOL;
	}
	public static function printSelf() {
		echo self::$name.PHP_EOL;
	}
}

A::printStatic();	// ClassA
A::printSelf();		// ClassA
B::printStatic();	// ClassB
B::printSelf();		// ClassA
C::printStatic();	// ClassC
C::printSelf();		// ClassC