Self-inspection raises the bar
One in 11 of the 2,054 schools inspected last term was judged inadequate.
This included 83 which were placed in special measures.
On average fewer than one in 12 schools was judged to be causing concern during the past three years.
More than 60 per cent of schools were judged to be good or better last term, including nearly 10 per cent which were found to be outstanding.
Mr Smith said: "The new inspection arrangements have raised the bar, and rightly so, but not out of reach."
Chris Keates, general secretary of the NASUWT, said: "The constant moving of goalposts to define what constitutes satisfactory or unsatisfactory, means that teachers and headteachers increasingly are setting less and less store by Ofsted's pronouncements."
John Dunford, general secretary of the The Association of School and College Leaders (ASCL) said most heads believed the new system of shorter inspections was "an improvement".