The boys (and mom and dad) get this perplexing question so often, but it's the hardest thing to answer. The more appropriate question might be, "What are you not learning right now?"
The boys are both starting to remember what they knew as toddlers: Learning happens all the time, everywhere, whether you like it or not. We learned about the different parts of plants that we eat while meandering through the produce section this afternoon. We learned about the muscles in the human leg when mom tore one a few weeks ago. We learned about brass instruments when we cleaned out a closet and found mom's old saxophone. We learned about death when we had to put down our dog of 15 years last month. Learning is life, life is learning.
I could tell you what we're purposefully learning, I guess. Short and long vowel sounds. Everything you never wanted to know about nouns and predicates. Multiplication. Early reptiles and fish like Dunkleosteus (the boy's favorite - Google it) that lived during the Devonian period. How green beans grow. What happens when you mix primary colors. The history of Carnivale! in Brazil, the Incan people, and the Yanomami hunters of the Venezuelan rain forest. Why The Phantom Tollbooth is one of the greatest books ever written (it is, trust me). Building volcanoes that erupt.
The problem with lists like that is it makes everything sound so segmented and clinical, when in fact, every one of those things are linked somehow, and we usually find ourselves wandering happily from one interest to the next. It's not that we don't use textbooks and worksheets, it's just that I never know where we're going to end up. But it's always enlightening, and never where I would have gone myself.