Al Mohler's post on this topic is a nice follow-on from my posts on the 6-finger exercise, and my synopsis of biblical knowledge to prepare children for high school.
I'll reflect on my own history of learning the Bible.
It probably wasn't until my later teens that I started coming to grips with the flow of the Biblical narrative (I know that it is not just narrative, but the term will do). This was by sheer dint of perserverance, and thus inefficiently attained on my part. Nowhere: not in Sunday School, youth Bible studies, church sermons, school religions education efforts (both lunch time club meetings and formal lessons) was I formally taught the lay of the land, Bible-wise.
I remember reading Zechariah at about age 14. I couldn't place this strange book; I had no concept of the overall structure of redemptive history and literature. It would have made far more sense if I had known at least that Zechariah was a 'minor' prophet, contemporary of Haggai, wrote about 520 BC and 16 years after the return from Exile (thus, after the events of Ezra-Nehemiah), looking towards the messiah, after Israel's many centuries of waiting. Also it was written long after the Psalms and David's reign, and also (not as) long before the coming of the Messiah.
But, for much of this period, the Bible was largely a mystery. Not even the Scripture Union notes that I used helped. They were of devotional assistance in the micro-detail, but the overall picture was not well formed.
I think that even a one-lesson Bible overview for later primary school children would be a great thing. It could be done interactively like the 'Walk through the Bible' programs, which takes one day for each testament, so could be quite a fun-filled and interesting approach particularly for younger people.