It looks like it's working in my current game as well. Although I am using a vehicle that was purchased out of buy mode, and it's sitting in the driveway.
All I had to do is select the teen, and then click on the parent and then select Ask for help learning to drive.
It might be that the Motive Mobile isn't allowed to be used for teaching a teen to drive? Like others have suggested, try using a different vehicle?
MrsFlynn