LEARNED VS LEARNT

The British English way of the past tense word learn is learnt. The American English way of the past tense word learn is learned. 

"Learnt" is more used in UK and Canada while "Learned" is more used in USA 

In addition, either term can be used as an adjective ("the learnt material" vs "the learned material") following the same rules.

Also, there is a 2 syllable word, learnéd (though the accent on the e has been more or less completely dropped since the advent of modern English, meaning you'll only see the accent in Shakespeare's works and that of his contemporaries or predecessors). "Learnéd" (pronounced learn-ed) is an adjective meaning that the subject has done a lot of learning. It is more or less synonymous with "wise."

http://wiki.answers.com/Q/What_is_the_difference_between_learned_and_learned

Learnt" and "learned" are two acceptable forms of the past simple/past participle of the verb learn, which means exactly the same thing. Learn is an irregular verb in the British English where the past tense is spelt with a ‘t’ at the end - [learn/ learnt]. Conversely, Learn is a regular verb in the American English where the past tense is spelt with a ‘ed’ at the end - [learn / learned]. Thus, neither is incorrect as “learnt” is more commonly used in the British English, and “learned” in American English.

Using anyone of these two forms are correct and is up to your preference. However, you would want to use the one that is more widely used or accepted in your country. When using any one of these forms you must use it consistently in your writings and don’t interchange your use of them. In other words, avoid mixing the “ed” and the “t” endings in your writings.

There’re other forms of verbs of the past simple/past participle in both American and British English. Some of these are: burned/burnt, smelled/smelt, spelled/spelt, spilled/spilt, spoiled/spoilt, dreamt/dreamed, leant/leaned, smelt/smelled etc.