Nobody else has touched on this, and as an American, I'm not sure how it translates to European educational systems, but isn't 7 a late start? In my experience, this is a problem that I had with my kids when they were about 5, in kindergarten. I don't think it's a problem problem, but you may find yourself dealing with some age issues later on... an 18 yo junior in hs comes to mind. Just sayin "be prepared"
To answer your question, in my experience, this is the kind of thing that requires intense 1-on-1 time. Just like cleaning their room or the after school routine, homework and school is a process that needs to be taught.
For my own kids, I always sat with them, body contact (whether sitting on my lap or thigh-to-thigh next to each other), arm around and worked on the homework. it's a protection stance (I didn't really think about it at the time, but in retrospect that's what it was). We'd work thru the questions. When we'd hit that wall, then it's time for encouragement. "cmon, man, you can do this. you've been saying your ABC's since you were a baby, so lets try it again." and we'd keep at it until there was some kinda success, then of course the 'attaboys'.
I would recommend as much of the same as is appropriate for the relationship. Sit close, teach the kid how to do it, support them thru a few examples. then once they get the hang of it, you can walk away. It may take a couple sessions before they're ready to fly on their own, but with the right motivation, they'll get it.