Verbal communication - not the same as written. Superb writers are often poor speakers; and smooth talkers often can't write properly....
Context - very often missing from general studies of a foreign language.
Logistics - Verbal communication best taught one-to-one - there is only so much a teacher can do when the ratio is 35-1.
Deep-Brain Automatic Responses - Necessary for true communication, but largely missing with students of a radically different language - such as between eastern and western languages.
Vocabulary - Not exchangeable on a word-by-word basis, but this fluid concept takes a lot of time to sink in.
Foundation of Basic Grammar - Important, but difficult to mesh smoothly with the moving and imperfect targets that languages are.
Group Repeat - Logistically useful, but many in a large group fail to get it right or even to participate.
A-B-A-B-A-B Chain Practice - Maximum speaking time for students (outside of pair work that is), but with the drawback that the students are talking with each other and not with a native speaker (who can, however, correct pronunciation and intonation while monitoring the conversation practice as it progresses through a group of students - best not much larger than about 15. (Around six or seven students is much better of course.)
Teacher and Student One-to-One Practice - Opportunity for students to speak directly with/to a native speaker, but with the drawback that students can only practice half of a conversation at a time.
Reading - Reading stories and other interesting material that is. Textbooks are often clinical and devoid of the magic of interesting conversations.
Listening - Fairly easily done with modern technology (electronic files played back on cell phones, etc.), but students need to push on even when much of what they're listening to is (at first) flying by with little comprehension.
Pair Practice - Logistically wonderful in that a large group can all be practicing a language simultaneously, but dangerous in that the students don't fully know if what they're doing is accurate in content, pronounced correctly, or with sensible intonation.
Culture - Vitally important, but often missing from textbooks which tend to use Frankenstein text with the context and life stripped from it.
Reset-Return to Pre-Word Thinking - Non-Verbal Pure Thought Utilization of Target Language Vocabulary - Words, at their best, are clumsy tools to express non-verbal thought processes. Non-comprehension of this vital element of language and communication (not the same thing) leads to losing the meaning and then mechanically using words, resulting in nonsensical usage and sophistry. Ironically, this is more of an issue for native speakers of English than foreign students of the language....
Lyle (Hiroshi) Saxon