To be fair i dont think the idea is that you train someone from scratch in 12 weeks, they are talking about the assessment of an experienced worker over a twelve week period.
i served my time 100% on the job then got assessed after to get my NVQ, mainly so i could get the correct CSCS card. At the end of the day you can do a three year college course you'll still know sod all until you get on site and learn in the real world. I know that these NVQ assessors who come out to site don't require much but neither do they in a college classroom. its all the same just another way of achieving the same end.