BrE vs. AmE Spelling
Read about some of the differences between the spelling systems of the British English and American English languages, so that you are consistent in your spelling throughout the writing task of the TOEFL.
BrE vs. AmE Spelling

One must admit that spelling in the British and American variants of the English language differs in many aspects. The main characteristic of the American English spelling system is its modification to become simpler in comparison with the British English.

• The letter combination –our in BrE at the end or in the middle of the word is often changed into –or in AmE: colour – color, favourite – favorite, honour – honor, neighbour – neighbor, etc.

• The verbs with –se at the end often have –ze in the corresponding American equivalents: analyse – analyze, criticise – criticize, memorise – memorize, etc.

• Single -l has a tendency to change itself into double -ll in some words in the American English: enrolment (BrE) – enrollment (AmE), fulfil (BrE) – fulfill (AmE), skilful (BrE) – skillful (AmE), etc.

• The letter combination –re at the end of the nouns in BrE is changed into –er in the AmE: centre – center, metre – meter, theatre – theater, etc.

• The –ogue letter combination at the end of the words in British variant of the English language is simplified to –og in the American English: dialogue – dialog, catalogue – catalog, analogue – analog, etc.

• In some words –e- is dropped out from the original BrE words with  -ge- letter combination: ageing (BrE) – aging (AmE), judgement (BrE) – judgment (AmE).

spelling• The nouns with the final –ence- in BrE are usually written with –ense- in AmE: defence – defense, licence – license.

• Finally there are some inconsistencies between specific words, such as

jewellery (BrE) – jewelry (AmE);
draught (BrE) – draft (AmE);
pyjamas (BrE) – pajamas (AmE);
plough (BrE) – plow (AmE);
programme (BrE) – program (AmE);
tyre (BrE) – tire (AmE) and some others.