I teach English in Bulgaria. My students (age 7 to 18) have a horrible problem regarding the writing. Usually after having a lesson I require the new words to be written couple of times. This is their homework. And they do that. However, a week or two after they simply can't write the word correctly. They know the meaning though. We drill the words in class, we repeat them many times, sometimes I show them a picture of the word on the screen with the spelling under it just to make their lives easier.
Question to the experts with experience:
1. What can I do in order to improve their writing skills?
2. Should I require them to write the words more times?
3. Any interesting games where the aim is remembering how to correctly write the words?

Thanks a lot in advance.