For 10 examples you're getting a 25-cent coin from a coin dispenser. You can keep it or you can use this money to buy Internet access. My OpenWrt router is connected straight to coin acceptor. For one coin you're getting 30 minutes of Internet on all devices (iPad and PC).
Since it's all automated I don't need to involve too much into education process. Math score in school has greatly improved, the kiddo solved thousands of examples.
Coin dispenser is proprietary (found on ebay, one of popular model), so I literally had to hack the USB protocol. The coin acceptor had no USB interface, so I had to introduce one. I've connected this USB to my OpenWrt 32-bit router, which is also ARM - so I had to hack some USB libraries along the way so my binaries can work with USB right from OpenWrt.
One of the advantages - there is no such thing as unlimited Internet. You always need to do some work to get it. Another one - there is interruption moment when it's over. There are lots of other good things. Like you can control the number of examples that needs to be solved. How difficult they are. Kiddo also understands what money is and how easy it is to spend money and how hard it is to earn.
I'm looking for co-founder to turn it into a business.
But I think even simple button that activates Internet for 30 minutes would work, since it introduces interruption between "consuming flow".