The difference between language acquisition and language learning is so profound that researchers who study neurolinguistics, which analyzes how language impacts the brain, have found out that the brain processes the two methods differently. The area most active during language acquisition is called the Broca's area in the left frontal cortex, whereas language learning mainly takes place in the Wernicke's area in the left temporal cortex.
Language acquisition involves absorbing language at a subconscious level through interactions with other people and the surrounding environment. It is accomplished without the direct assimilation of grammatical rules. This is what happens when children learn their first language or languages from their parents or caregivers. They simply listen and repeat what they hear. They get a feel for the correct usage of words, sentences, and the intricacies of rules without anyone sitting them down and teaching them. Young children can also often learn second languages through acquisition when teachers focus on communication and interaction rather than the formal memorization of rules.
On the other hand, language learning involves the direct instruction of language with an emphasis on rules and patterns instead of communication. It is not recommended for very young children because it presupposes a rudimentary knowledge of the language that is being taught. In fact, language learning is a less effective method for adults too than the more immersive experience of language acquisition. In language learning, students study syntax, phonology, reading, and writing. They may learn the language sufficiently to do well in standardized testing, but they may still have difficulty speaking and writing correctly when they are immersed in an environment in which they have to use the language in the course of everyday life.