where to go in Germany for a week with my grandson

I love the towns around the Baltic too - Lübeck, Wismar, Travemünde Kiel, There’s a fascinating Viking ship burial museum at Haithabu (sp?) in Schleswig Holstein.
I would also love to visit the Harz mountains as my parents met in Goslar, but that is just me.
At the risk of offending anybody from Bavaria and the Deep South, the accent can be a bit impenetrable (ducks hinter dem Sofa)
etc
But rather than just doing sightseeing, could you perhaps incorporate one of his interests too?

Dresden is a beautiful city way in the East of Germany. On the river Elbe, there’s lots of museums, galleries, shopping , river trips. Completely rebuilt after WW2 in baroque style it’s certainly worth a long weekend. I also liked the baroque city of Potsdam which is near Berlin, so many historical sights and museums, beautiful parks. If you want to go somewhere for a week it may be better to choose a couple of centres - Helidelburg, the Rhineland etc.

Another vote for Aachen, Dusseldorf and Koln. A really beautiful part of the world

Lübeck, is a lovely town, actually i was born there. Theres a nice beach area, travemunde, a short train ride away. Hamburg has become very ‘ in’ and isnt far. I suppose it depends on where your local flights go to, lubeck has an airport and ryanair used to use it for hamburg but pulled out from stansted at least some years ago.

I would probably stay in the north: Lubeck, Hamburg, Rugen Island (seaside resort) are all good places to visit. If you go on YouTube I'm sure you'll find videos of the major tourist attractions. Or TripAdvisor will give lots of helpful information.
Let us know where you decide to go.

JaneAnn, did you know that the national German airline is opening up two new routes from Glasgow to Frankfurt and Munich starting in March.
I assume you are in Scotland, as you mention "Nationals"
I studied German at university and I had no problem understanding the language in Munich and Nuremberg.
On the other hand, this info may be totally useless to you

What a lovely idea.
There are many attractive places to visit in germany, some have already been suggested. Sometimes slightly smaller places might be More authentic, friendlier, the rhineland or moselle are not too far and very scenic with lovely old villages along the banks, aachen is a nice city, very historic, dusseldorf, cologne ( koln) . Public transport is fairly cheap and very efficient so its easy to get around. I think wherever you go will be fine though try to avoid the south, its lovely there but their german dialect is hard to understand. We arranged for our daughter to spend 6 weeks with a cousin in the south. They got her a job in woolworths on the counter but she could hardly understand a word though she managed by some miracle, to do reasonably well in her exam. Have a great time and i wish your gs well in his exam.

We liked Heidelberg. It has a castle and a zoo, and the river, and you can walk up the Konigstuhl (sp) for the views if you're feeling energetic!

Freiburg.Also not very big,easy to get around on the trams and a beautiful Centre overlooking the Cathedral. DD was at uni there and when I visited I was quite happy to potter around on my own.I felt very safe and at home there.

Weimar. Not too big, lovely buildings, history, literature, and the Bauhaus.

As much as I would like to invite you to my part of the country, the rural South, I would recommend somewhere like Hannover, Kassel, or even better, Bremen and Hamburg. In fact you could combine the two.

If he's into fairy tale castles and wine-tasting, then he can come this way, but I expect Hamburg and Bremen have much more things of interest for boys. Boats, football - if you are going in the late spring or summer, beach walks and trips to the islands, castles, and lots of history, shows, fun and shops.

It might get expensive, though.