learned is the correct spelling in American English (and for Canada, too) Whether you’re saying you learned something or learnt something, you’re talking about the same thing—the process of finding out, acquiring, or retaining knowledge or information. The only difference is that the way you spell and pronounce it says something about ... More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.