For reading comprehension I would just look for free worksheets online. Here are a bunch of worksheets that have a passage on one page and multiple choice questions on the next. They are from a website called
www.havefunteaching.com. FWIW, I just googled reading comprehension multiple choice.
First Grade (~25 worksheets)
Second Grade (~60 worksheets)
Third Grade (~60 worksheets)
Since you said he just wants to show mastery and get that feeling of accomplishment, I would give him one from each grade at first so as not to blow through them. Obviously, if the first grade is just painfully easy don't push it.
I have no experience with this stuff because my four-year-old is the exact opposite right now. She reads for pleasure if at all. This is too close to work for her. I once asked her if she had fun doing something like this. She looked at me like I had two heads and said, "It was work. Why would I have fun doing work for nothing?"
With math, I recommend just exploring the numbers. We have a large set of cuisenaire rods on our dining room table. (I just got them back out after forgetting to do so for about the last 6 months.) DD also loves skip counting, and I cannot think of anything wrong with sufficiently memorizing how to skip count 2s through 10s. Then, theoretically, we look at the patterns using cuisenaire rods. Recently, DD looked at the relationship between the 2s table and the 3s table. 2 is to 3 as 4 is to 6 as 6 is to 9 etc. DD does know what an addition problem looks like on paper (actually on a foggy car window) but I also want to keep math about number sense and patterns right now. We keep math in our head and in our hands and leave the paper. With double digit addition she looks for patterns. 10 plus 15 is just two tens plus five. 10 plus 10 is 20. 20 plus 5 is 25.
There is a math curriculum called Miquon that is supposed to go with cuisenaire rods. I have never seen it, so I cannot comment on the writing requirements, but I have read great things about the program in its development of number sense. I suppose if you had the rods you could give him a bunch of problems written out and ask him to replicate them along with the answers using the rods without writing anything down.
For writing, I throw my hands up. DD's school does not do any writing. Last week I decided to let her use an iPad app and it has helped with the lowercase letters. She came up with the idea of tracing the letter on the iPad and then practicing the letter on the magna doodle. So, that was a win. She seems to be delayed in hand strength and the VS perception needed to form the letters correctly. But, the app seems to be helping.
