It's not your fault... most of the time!
Your students speak an alien language... they are young, they think literally and without much academic imagination. Your subject though is NOT literal nor is it tangible... it's an abstract concept that too often defies logical analysis through young eyes.
Teaching any foreign language in Thailand has an added hurdle because there are no connections between their native language and what you're trying to teach. Europeans can learn English more easily because there are many things that connect the two different languages... most importantly the shapes and sounds of the letters!
Another thing to think about is just how important a child thinks learning English is. Probably not very! The further away from Bangkok and other large cities you go, the more apparent it is that English is just something bewildering and annoying that Thai kids try to bluff their way through before playtime or going home time.
Vegetarians eat vegetables, so zombies are humanitarians, right?
The rules of the English language... there are none, really! Just do an investigation on phrasal verbs and you'll quickly understand why Asian students scratch their heads and zone out in their classes! And don't get me started on ditransitive construction grammar... or adjective order. Grr! What we take for granted as native speakers is bloody hard work for those who aren't.
One of the mistakes that many English teachers make is the compulsion to correct kids for things that don't necessarily need immediate attention. Instead of teaching them good English language skills, it's often easier to correct bad habits they've picked up or mistakes they make. This isn't always good teaching practice and it doesn't help the students, especially with their confidence.
In a recent forum debate I took part in, there was a teacher who claimed that people (like her, of course) were good at teaching English because they explain things in great detail. I put forward the argument that explaining things 'in great detail' can be counter-productive and end up doing more harm than good, but it fell on deaf ears.
"I taught that last week. I'm amazed the kids haven't learned it!"
If you've ever worked at a Thai school you'll hear kids in the classes near you chanting. They'll be chanting their Thai lessons, English lessons, science lessons and chanting their chanting lessons! It's how Thai kids learn. While repetition and memorizing stuff isn't a bad thing, it's too heavily relied upon in Thailand. It's a lazy way for teachers to teach stuff rather than a critical way for students to learn stuff. Also, the chanting exercises leave more time for teachers to mark homework and check in with Facebook, right?
And the further away from the big city you go, the worse the Thai teachers are. People who are hired to 'teach' English are very often poorly educated in English skills themselves. Thai school owners and administrators have no way of knowing how competent or qualified teachers are, so there are tens of thousands of Thai 'English teachers' who aren't up to the job of teaching.
Another thing slowing down the retention of English language in Thai students is the absolutely appalling standard of textbooks on offer. I've seen them all and they are ALL rubbish. They range from simply inaccurate to liberal trash about climate change! It's horrifying how irrelevant and disconnecting the materials are.
Yet another stumbling block is the lack of freedom native English teachers are given to make changes that would help the kids learn. Many schools want the expensive farang hire to 'stick with the program' rather than come up with imaginative and useful exercises that might actually work. And even if you are lucky enough to be given some scope to make your classes more appealing and useful, the back up from the school may be so bad that you end up spending your own hard earned cash on materials to make things happen.
If you're feeling frustrated that your message isn't getting through or your lesson plans are just a waste of time, don't take it too hard. There are many obstacles in your way that you can do almost nothing about.
So, there we have it. Lots of good reasons why teachers are struggling to get the job done and the good news is that none of them are your fault!