Many students cannot speak and write Italian because they don't study hard and don't know how to memorize words.

Just today I asked a student to go to the board and write a sentence and she could not spell the word. I tried to help her with spelling the word into Italian of course, since I was supposed to teach Italian, but the girl didn't even know the Italian alphabet. I'm talking about an intermediate class, which means that she should have already memorized the Italian alphabet at least.
Students should learn to self-assess and if they think they cannot be at the same level of other students, it'd be better to review the whole content and move to another class.
They think it is enough to read a dialogue or a reading once and then they will remember it.
They translate the text and then don't go over it. That's not at all enough to master a language. After you have translated the text you should try to summarize or paraphrase it using your own words. In this way you are challenged to speak. I know it is strange to speak alone at home but this is the only way it should be done if you have no one at home with whom you may speak Italian.
 Memory needs to be trained. It is like a muscle.
Think about the athletes who are competing in Beijing during this period. Do you think they only train one day in a week? Or maybe they train the whole week and then they have a rest for 3 days? I don't think so.
Repetition is essential to remember the words over a long run. This is not easy to implement, but with a little discipline and organization you can make it work.
If you learn new vocabulary with a newspaper and dictionary, it is a good idea to go back to last month's articles with no dictionary and see how much you understand.
Using words in context enhances greatly the chance you will remember them.
It is always a good idea to learn words with a phrase as an example.
Foreign language vocabulary is not made of random combinations of letters. Many words in a language are derived from other words in the same language. These words can often be grouped around a common root. If you learn the root and recognize it in new words, it will considerably help you to remember the new word.
Italian has lots of verbs to memorize. If you study without any mental order you won't know how to use them.
Learning a language needs will and sacrifice. It is not enough that you come to school and stay in my class. I can explain you the grammar. I can help you practice it but you must study hard and with discipline. You must learn to depend on yourselves. Don't wait for the teacher to tell you what to do. You are not kids. You are adults who should already have a study strategy. Good luck!