There are many verbs like this: dreamed, dreamt; spoiled, spoilt; kneeled, knelt, etc. When used as a verb, both `learnt’ and `learned’ have the same meaning. You can say:
* I have learned/learnt a lot from Ganesh this semester. * Our new bowler has learned/learnt to bowl the `doosra’.
According to some scholars, `learned’ is more common in American English, while `learnt’ is used frequently in British English. When `learned’ is used as a verb, it is monosyllabic. In fact, some people pronounce it like the word `learnt’. Others pronounce the final `ed’ like the `d’ in `dip’, `deep’, and `do’.
When the word `learned’ is used as an adjective to mean `scholarly’, it is pronounced as a word with two syllables. The final `ed’ is pronounced like the `ed’ in `wanted’, `grounded’, and `hated’.
* As expected, the learned professor bored the poor students to death.