It is important to have a general understanding of children and of child development so you can plan your lessons accordingly.
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It is a good idea to have at least a basic knowledge of the language in the country in which you're teaching, since the children may be quite young and have a low level of English.
3

It is important to try and only use English the entire time in the classroom with the children. If they don't understand something you say, show them. Demonstrate as much as possible and remember to use many games, songs, and activities to get them moving.
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Never force the children to speak. They should enjoy the lessons and not feel stressed about going to English class. The best way to get them to speak is to show them a picture and to say something like 'Is this a bird, or a cat?' and try to use a word that they already know. They usually want to speak it then.