This reduction reflects both the shortage of high - quality offerings brought to the market and also widening of expectations between buyers and sellers. (seekingalpha.com)
I think one trend that isn't listed here, and is important, is the ever widening gap between high poverty and low poverty students at the 12th grade level. (aheadoftheheard.org)
But the 1970s that process has slowed, due presumably to the decline of British manufacturing, with the gap widening in the last 20 years. (politics.co.uk)