18 May 09
01 Jun 09 8:56 pm
Generally speaking, you will not be penalized for this. There are some more things to consider rather than being penalized by the SEs when intentionally creating internal duplicate content:
Site structure is an extremely important part of both usability and SEO. It is important that your site structure is consistent, logical and predictable.
You state that "I want both to be able to rank".. for what? If the key phrase you want both of these pages ranking for is the same or very similar then 9 times out of 10 you are much better canonizing the URL to be one or the other and allowing the SE's to index and rank that page powerfully, rather than leaving it up to the SEs to check your internal pages with duplicate content and decide.
Generally speaking two identical pages on one site will not rank for different keyphrases. There are exceptions, but these are rare.
You would be better offering the visitor the option of what version to read through the prominent display of a "relevant lesson" link on both pages linking to eachother.