For adults, learning a new language can be painfully slow and often a frustrating experience. While everyone would like to quickly acquire the ability to converse in a foreign language, the reality is that it is not easy - there is a whole new set of rules to learn, let alone thousands of new words and expressions. It can be very burdensome to have to, in effect, go back to grade 1 and start all over again.
Teachers also have to be aware that adults do not learn the same way that children do. Sure, there are times when learning is the same, but often it is very different.
Adult learners are comfortable with abstract thought patterns. They like to call on their life experiences and know what they expect from an ESL course. Adults have developed methods of learning that work best for them and, when they apply those methods. Their discipline is far more evident than one sees in children. Partly, this is because their brains are fully developed but they also have better motivation.