GCSE's 'must maintain standards'
22 August 2013 Last updated at 10:48 BST
There has been a drop in the proportion of GCSE exam entries awarded top grades, for the second year in a row.
Head teachers say changes have caused "a lot of turbulence" in grades.
The chair of the education select committee, Graham Stuart, said: "Any change to examinations tends to lead to greater volatility."
The Conservative MP said schools have "less predictable results" but the changes ahead are important to "maintain standards".