Verb Morphology
Check out main differences between American and British English ways of making the past participle forms of some irregular verbs.
Verb Morphology

1. Such verbs as learn, spoil, burn, dream, smell, spill, leap, and others, can be either irregular (learnt, spoilt, etc.) or regular (learned, spoiled, etc.). Although in British English both variants can be used there is a tendency to use irregular forms. However, in American English regular forms with the –ed ending are used almost all the time. Compare:

Infinitive              Past Participle (BrE)                          Past Participle (AmE)
  bust                                         bust                                                              busted
  get                                            got                                                                gotten
  lean                                          leant/leaned                                              leaned
  learn                                        learnt/learned                                           learned
  saw                                          sawn                                                          sawn/sawed
  smell                                        smelt                                                          smelled/smelt
  spill                                          spilled/spilt                                               spilt

2. The verb fit has usually a past participle form of fitted in British English but fit in American English (however, when the word is used in the sense “to tailor” then fitted is also used in American English).

3. In American English the verb get is quite often used in the meaning of “have” in the collocation have got (in British English simply have is used). In this case past participle will be have got (even in American English). Compare:

British English                                          American English
I have a ticket.                                                    I’ve got a ticket.
I have had this ticket since Monday.           I have got this ticket since Monday.

4. In American English many irregular verbs allow to mix their past participle and past simple, while in British English it happens rarely. For instance, spring-sprang-sprung (BrE), spring-sprang/sprung-sprung (AmE).

There are some further differences, but they are minor, quite complicated and used locally or specifically by some groups of people; therefore, not very important to your TOEFL preparation.