Child Theme vs Parent theme index.php ?

Hello, I am fairly new to WP development and am running the current version of WP on MAMP just trying to learn my way around themes. I am running through an exercise trying to play with the thematic framework. I am using a child theme, I heard that if you copy the index.php file to the child theme’s directory, WP should reach for that before grabbing the index.php in the parent themes directory. When I copy the index.php file to the child theme’s directory and edit it, it doesn’t change my theme at all. If I edit the index.php file in the parent directory, it works fine. Is my hierarchy wrong? Should my theme go for the index.php file in the child directory first? Sorry for the n00b question. Seeing as this is my first post, hello all.

Thank in advance (hopefully).

WJ