British vs American vocabulary

English is not one target. British and American English differ in spelling, pronunciation, and — most visibly — everyday vocabulary. Neither is "more correct"; what matters is being consistent and knowing that the same object has two common names.

Which variety to teach depends on your students' goals — American English dominates film, technology, and much of the internet; British English is common in Europe, in exams like IELTS, and across the Commonwealth. Pick the variety that fits where the class is headed and keep it consistent — while making sure students can recognise both, because they will meet both constantly.