My daughter has always loved a challenge.
For instance, regarding the counting, and adding in an engineering challenge, try something like this:
Gather some supplies like plastic wrap, straws, foil, paper egg cartons, T P tubes, tape, etc. and have son make a boat. (If this would be too difficult or frustrating, modify to his level).
The next challenge is to see if the boat floats, first, and if it does, how much money (coins) can we put on it, counting one at a time, until it sinks.
If this is easily accomplished, up the challenge by taking out the most utilized item(s) and see if he can make a boat from other items. Or challenge him to use less items, like only use three instead of four items.
Try to limit or eliminate your help and see what he comes up with.
Another challenge my daughter liked was to make a ball run, and use whatever balls you have available (small rubber balls from gum machines are my favorite). If/when this challenge is easily met, time the descent and challenge him to find a way to make the ball take longer to get to the floor, but the ball run can't be made any taller.
You get the gist.
Also:
The Khan Academy has a wonderful progression of math skills that might be helpful in making sure he learns the math that he needs.
They have also introduced a grammar program, though he may be too young for that, not sure.
Spelling City is an online site that has games to help practice your own spelling words, or use their lists.
Sonlight (and their secular counterpart, BookShark) has probably one of the best history and science curriculums out there. If nothing else, it is an excellent book list for readers and read-alouds that can be found at the library.
A program called Good and Beautiful has a great language arts program (though I didn't use it in the early elementary years). It can be downloaded free.
I also like Singapore Math, Standards Edition. Very thorough and rigorous math program.
Good luck, I hope your day is going well!
Apple