International schools are normally made up of a multi-national student body, many of whom English is not their mother tongue. Many parents choose to send their children to an international school not only for the international curriculum (US, UK, Australian or IBO) but also for an excellent opportunity to learn English. Of course it would be nice if every learner that came into our class knew some English. However, sometimes this is not the case. I have found that learners with very little English language need a lot of demonstration of the tasks to be completed, which is hopefully what is happening anyhow when teaching younger learners. Young learners are ALL learning how to read and write and need simple instructions anyways! However a problem can arise when confronted with teaching a Year 6 non English speaker in Science for example. Instructions need to be clear, concise, demonstrated where possible and in extreme cases front loading (in the way of notes, summaries or short discussion about the task to follow, pictures or diagrams) may be required for the learner. The goal of the teacher is to get the learner to understand the 'gist' or purpose of the activity/task and why they are performing it. Language development will follow.
One thing that is important is that the learner is competent and confident in communication in their native tongue. I have found that 100% immersion is the most effective way of learning any language- speaking from experience.
Probably the most difficult challenge teachers face is when a non English speaking learner is 'thrown in' to a class - mid year/term! Individual Learning Programmes can be implemented here with goals and targets set by teachers and negotiated with students, and getting the parents involved too.
Of course ESL certification and experience in teaching ESL learners is invaluable, be it adults or young learners. Knowing the challenges an ESL learner faces prepares the teacher for developing and implementing strategies to enable the learner to make a smoother transition into the mainstream classroom.