There is a big, big difference between someone who struggles a bit and someone who is a "hopeless case".
Hopeless cases are just that. No chance. You could throw millions at their training and it wouldn't matter. They are rare beasts though, but when you meet one. You know instantly!
Someone who needs extra support? Well, that's what we're paid for. As long as they are aware that it will take them a bit longer, but that you will be with them every step of the way, then fine.