Harold/Karyn,

There are indeed similarites between first and second language acquisition (though they are not the same). Adult learners may need/want instruction by a teacher, but it doesn't alter the fact that the real learning or 'acquisition' happens below the level of conscious activity. This is why immersion can be highly efficient - learners can focus on doing other useful tasks without explicit reference to the target language. It's a true case of learning by doing.