Re for example the listed number in the Preflight procedure (Boeing 737) for the Standby Power switch I wouldn't have a clue but I sure would pick it up on a scan flow. You don't have a challenge and response for every single item a pilot looks at or even sets up. However, many flying schools design checklists so that almost every item is read out. At a typical VDO cost for a light single at four dollars a minute (more for a twin) watching a student reading a lengthy checklist on the ground with the engine's running is another wonderful money spinner for the instructor and the flying school.
As someone said earlier a scan flow system of checking items takes a few seconds if the student is taught correctly - and that means encouraging the student to sit in a cockpit without an engine running so he can learn the scan. There is one well known flying school in Victoria that does not permit a student to sit in the cockpit of a C172 on the tarmac without the presence of an instructor.