Ask HN: Any way to monetize a simple game?

I have a simple math practice game at http://zetamac.com/arithmetic/.

I've had it up for about 5 years now and have never made any money off of it so I was just wondering if there's any reasonable chance of me making anything off of it. It gets played about 5000 times a week (~500 uniques).

I've tried applying to AdWords, but have been rejected because they claim the site is "Under construction". Presumably it's not enough text content, anyway. Are there any ad networks that would be better for this sort of thing? Should I instead look for specific sponsors who can just sponsor a single ad for a while? (Also, about how much would you expect would be reasonable to make from ads from a site like this?)

I've thought about adding features and charging for them, but I couldn't really think of any that would be interesting enough to make me want to pay for them, so presumably most other people wouldn't want to either.

Any suggestions would be appreciated.

You could, you know, look around for ad networks.

Then it occurred to me that this arithmetic would be much easier if I had built up to it, i.e. I was used to doing sums like that.

So, with that in mind, perhaps you need to offer more? I mean, a lot more. Ways to track my progress as I do build up, ways to give me good places to push the boundaries of my mental arithmetic. I mean, you could go on extending it and making more useful. You could dig out research for the best way to get the user to learn.

I'm thinking along the lines of the "goal" to be able to perform sums like those Japanese students who use abacuses to solve massive sums very quickly even once the abacus is removed.

There are plenty of interesting features you could add to it! Make people grow from it!

I would imagine your target audience would be the younger generation with their parents (schools?) paying their son's education interests. I could imagine every parent seriously considering purchasing if their child was interested.