Students' motivation (or the lack of it)

First of all, hello to everybody

I'm kind of new here although I've been following this forum for some time. I registered because I really don't know what to do about my two students.

Namely, I give private classes and I've been teaching this 12 year old boy for almost a year now but our problem is that he's soooo not interested in English and he's taking these lessons only because his father obliges him too.

To make it perfectly clear, this boy is not the brightest person in the world, but he's not stupid either. His marks from other subjects are Cs and Ds mostly, he had C from English last year as well. We're making a really slow progress although he still hasn't fully grasped the usage and formation of Present Simple and Cont. I've tried everything, from bringing some board games, to using computer, talking about Harry P books (which he likes to read), movies, video games, literally everything but he's less and less motivated with every new lesson. When we talked about movies and v. games he kind of responded to the topic but the next time it was the same story. So, ok, there are some topics that interest him but these aren't unfailing springs so to speak.

I talked to his father of course, and after that the boy usually does the homework correctly but after 2-3 classes he starts making the same stupid he-go-to... kinds of mistakes. I can see that he's always lacking concentration and motivation and if you add to it his ...well, let's say, lack of talent for schooling, if I can put it that way, it all gets too complicated and exhausting for both of us.

The other boy is 17, he only wants to talk in Eng which is perfectly ok with me, but he also doesn't put a lot of effort in that, he doesn't think about what he's saying, I have to repeat the same thing over and over again and when I come the next time he doesn't remember a thing I said the previous time. He's simply trying to communicate (he's intermediate level) without thinking about grammar, words, etc. His mother wants him to take the lessons (so again there's a lack of intrinsic motivation probably) and I keep asking myself is it me?
Maybe I don't know how to motivate people.

Does anybody have any suggestions or similar experiences, anything that could help me (both to feel better about myself and to make my students feel better too).

This has been a long post but I hope you had the patience to read it through.

Thanks

My simple advice is to use games and activities to motivate the young ones and students' interests for the older ones.

I get this all the time with some of my private students. It's really hard to motivate someone who doesn't want to do it. So what can be done? There must be a way to interest the student! Well, there is a 10-year-old I've been tutoring for some time now. He goes in for hockey and dreams of becoming a professional hockey player one day. I printed out a short English-Russian hockey dictionary for him. And that got the ball rolling, it seems. I also gave him several printouts featuring the auxiliary verbs and the 5 major types of questions in English. I ask him to use the word list and talk about his usual hockey practice, using those printouts. And I always remind him that if he plans to play in the NHL one day, English is something he will absolutely need. That seems to get it going.
It's extremely hard to teach Russians English as there are no articles in Russian and the copula to be is almost never used. So I ask him to USE the copula when talking to me in Russian!
Of course, some people are just incorrigible. In that case, why torture yourself? Find someone else!

The more hands-on activities you do, the better. I'd try and get out of the classroom as much as possible.