I don't home school but as part of my DS school work he was asked to keep a journal (we took him out of school for the week). We got creative and put together a journal page or two for each day, each port, and each of the people I thought we would meet on board. For the latter, it was our stateroom host, our head server, our Cruise director, the captain, ect.. Each page had questions as where they were from, what their home country was like, what they day/job was, how they got there and some basic word translations in their language.
For each port we would visit a musem if possible, if not possible we would gather information on an excursion. We researched the areas at home so I had a good idea if a museum was possible. I also picked interesting excursions where he would learn something much like OP said researching Sting Rays.
It is one of the greatest Souvenirs we have. This next cruise, he is not missing any classes but, I am doing it again just because.
I would also take photos of him with the staff at
DCL and excursions. He then pasted that on their page in the Journal.
He still talks about the museum and the turtles in GC and the secret river excursion in Cozumel.
He will forever remember our servers and their history and cultural lessons (stories from their country).
BTW the DCL staff actually liked answering his questions and we respected their time, because they have very little of it to stop and chat. Our MDR servers were wonderful and after the first night volunteered new stories, or facts about their countries or studies.
There is a ton to learn on a Cruise, that was my take away.
Hope this helps, and have fun

have a great cruise!