My son mentioned that in class yesterday his teacher handed out a maths sheet to be completed during the hour. After 6 minutes, one of the girls finished, and shortly after several other children finished, too... They were given some extension work, but that was pretty boring.
I think you've highlighted a problem with preparing our children for the 11+. It divides the class into those for whom the work is old and boring, and those for whom the work is new and challenging. This is particularly true for Herts, where the schools are these superselectives, and people seem to tutor for longer, perhaps.
I don't know the answer to your question, though.
I'll be interested to see the replies.