DS1 does not have any additional educational needs. He has difficulties with self-organisation and remembering things, but has developed techniques to manage this.
He is academically able (got a specialist academic place at a partially selective secondary school) and fairly strong in Maths, English, Sciences & Humanities.
However, he does not seem to be able to learn languages. He has now been learning Latin & German for 2.5 years.
In German, he can manage the reading part (using guesswork & deduction) but struggles with writing, speaking & listening. He has been taught the grammar but doesn't retain this knowledge, and despite learning the vocabulary repeatedly, it doesn't stick. He has do to German GCSE.
In Latin, despite learning the vocabulary over and over (and over) again, he still seems to know only 50% of it. He has been taught the grammar at school, and seems to understand it at the time, but the following day/week this understanding disappears. I have seen him do translations; he mostly does this using guesswork. Bizarrely, he really enjoys Latin and has chosen it as a GCSE option. 
I cannot see how this is going to pan out. Does anyone have any tips? I'm planning to post this elsewhere too, in the hope that someone will have some advice that can help him.
If you are his German teacher or his Latin teacher, then I'm really sorry. We are trying our best to support him at home, but it seems to be going in one ear and out the other.