Wh do students have difficulty with english grammar in the english class

They say English is the most difficult language to learn. for every rule this is an exception. Schools don't teach the rules anymore and even had experimental ways to teach it in the 70's so the students did not know the rules when they had to go to the next school that might have taught the traditional classes. I have a hard time spelling for that reason but keep trying to learn where I can. and this program with is spell check is great. Anyway like the Chinese having to memorize their caricatures and the romance languages learning the tense along with feminine, masculine and formal and informal it is up to all to learn some way to communicate in a positive way with the world and it all takes work even if we have to take the initiative our selves. I like to read old books when the art of writing was in vogue. I look for old book not modern ones to see how it is to be for real. They are usually only 5 by 7 inches or little bigger and have the word in the title of grammar or English. I even found one in a 1890 house in Nevada. It used to be the school of the farms around the area. I have not used these books and is on my to do list after I get my family tree back past the 1890s. good luck.

As a non-native speaker of English and an English tutor-teacher, I can contribute to the question. English is not the hardest language. But there is such thing as transferring (I'm not sure about the correct term). It means that the learner transmits his associations, feelings, the rules of other languages and mess in his head into speech which leads to mistakes. E.g. 'you're' and 'your'. If students don't learn the difference, they may switch these two different structures because they look familiar. So, as a teacher you have to make your best teaching them systematically, so they won't mix up things. Which is hard. It sucks :(