* Contact classes have their limitations in that you, the learner, are exposed to the target language for a very limited time.  From a rough survey, it appears that most beginner courses run for three months with two classes per week, giving you an total exposure of 24 hours to the target language. Some offer even less.  Successful language learning depends on the amount of time you spend in contact with the language and the pace of everyday life does not always make this possible.  An effective on-line language learning program will bring the language to your home or office, giving you 24/7 exposure if need be. 


* Secondly,in contact classes you are not always taught what you want to know.  You are therefore in the hands of someone who presents what he intuitively thinks you ought to know


* Thirdly, taking the number of contact hours into account, adult classes are expensive.