At least in mathematics, after each video, they have a fairly sophisticated set of tests that are quick to pass if you’ve understood the concept, or that adapt

At least in mathematics, after each video, they have a fairly sophisticated set of tests that are quick to pass if you’ve understood the concept, or that adapt in difficulty to your level of understanding and attempt to fill in any gaps. It’s quite impressive. Kids can definitely use it to catch up or work ahead on their own if they are interested.