$_GET and URI Routing

[eluser]sixpack434[/eluser]
Hi guys, great if someone can help

i'm converting my old website to using codeigniter,the old method of showing lessons on the page is by passing the ID to the url. For example, to show lesson 10 the url would be

www.sitename.com/lesson.php?ID=10

I thought I can use uri routing to pass users to the new page if they try to use the old method e.g.

www.sitename.com/lesson/10

but this doesn't seem to work, my routing functionality is

$route['lesson.php?ID=(\d+)'] = "lesson/$1";

This is throwing a 404 Page not found error

Isn't it possible to solve this problem by way of routing?

Any help is much appreciated