It's similar to how motorcycles are derated.

In Europe there is limit to the kW output of motorcycles someone with a learners permit can drive, so in a lot of cases the output of a more powerful bike is limited so they can learn on the same bike to what they will be driving.

To achieve this on some bikes you can restrict the air flow through the carburettor, which can be as simple as adding a piece of cardboard in the right place...