Helen, the cure is that parents read to their children, and then encourage children to read for themselves. You can let the child learn written English naturally as their mother tongue, or you can teach it to them as a foreign language later on. And anyone who was forced to learn a foreign language at school knows how effective that is. In other words, it's exclusively the fault of parents, not of teachers. But saying "your parents were lazy" probably won't go down too well with your teachees, even though it may be true.
Quick apostrophe guide: use it ONLY when something belongs to someone else, or when a letter is missed out ("John's book isn't here."), otherwise don't use it. And how to encourage them to use it? Maybe a limit of 3 grammatical errors per page, after which you dock marks. That should encourage them to proof-read their work!