Schools which encourage pupils to take exams in "difficult" subjects are penalised by a system which does not reflect pupils' true attainment, Professor Carol Fitz-Gibbon, director of Durham University's curriculum, evaluation and management centre, said.
In evidence to MPs on the Education and Skills select committee she argued that the Government's value-added measure failed to recog- nise that an A grade in physics represented a higher achievement lev-el than the same mark in sociology.
Pressure to drive up results gives schools an incentive to persuade pupils on to easier courses. "The value-added tables as currently calculated undermine the sciences and this is a source of great concern in a modern economy," she said.
Professor Fitz-Gibbon also called for greater scrutiny of the actions of those marking papers. She wants candidates' names and their schools to be removed from papers before they are marked to avoid bias.
Stories of examiners claiming "I'll be finished with these papers soon, they are from Birmingham," or marking papers from "toffee-nosed" private school pupils more severely showed the need for reform, she said.
Scripts from each school should be sent to more than one marker to ensure that severe marking was not mistaken for bad teaching.
Professor Fitz-Gibbon, Anne Cole, head of Saltley school, Birmingham, and David Daniels, head of White Hart Lane school, London, were giving evidence as part of the committee's year-long inquiry into secondary education. Both agreed that assessment and accountability was in need of reform.
The Government's concerns over the lack of young people studying science subjects was highlighted in this week's budget. The Chancellor announced new measures to encourage foreign nationals graduating in maths, science and engineering in the UK to stay and work here.
A spokesman for the Department for Education and Skills said: "There are no easy subjects. We are consulted widely and we believe our system is the fairest available."