Learned or Learnt, it's your choice :)

Learned and learnt

The verb to learn means to acquire knowledge of, or skill in, something through study or experience.

To learn is one of those verbs with both an irregular  and regular form. (See the table below for some others.)

The past tense and past participle can be written as either learned or learnt. However, they not interchangeable, especially in the US.

Americans Demand (require you say) Learned

In America, learned dominates. The use of learnt as the past tense or past participle of to learn is considered a spelling mistake by many. It will certainly annoy many of your readers.

Brits Prefer Learnt

Outside America, learnt is more common, but learned is generally accepted. (This is almost certainly a result of American influence spreading.)

AUSTRALIANS.......  :) I like both of them. Academically, I prefer writing learned. It's your choice dear students.

Verbs with Irregular and Regular Forms

The following verbs (like to learn) can be regular or irregular:

Verb	Past Simple	Past Participle
burn	burned OR burnt	burned OR burnt
dream	dreamed OR dreamt	dreamed OR dreamt
learn	learned OR learnt	learned OR learnt
hang	hung also hanged	hung also hanged
smell	smelled OR smelt	smelled OR smelt
spell	spelled OR spelt	spelled OR spelt

As with learnt, the second form (e.g. spelt, dreamt) is more common in British English.