A lack of science experiments and specialist teachers is affecting state school teenagers' chances of winning places at top universities, a leading head has warned.
Universities are not producing enough graduates to become specialist teachers in areas such as science and languages, according to David Levin, headmaster of City of London School.
And children are not being exposed to enough practical science lessons to gain the knowledge they need to study it at a higher level, he said.
Speaking at a conference organised by the ARK academy chain in central London this morning, Mr Levin said: "Until the maintained system has a sufficient number of teachers in specialist subjects, in physics, chemistry, mathematics and modern foreign languages, the social mobility debate is not going to be advanced."
Mr Levin said that his school, a private school for boys aged 10 to 18, runs a number of master classes with state school students as well as a gifted and talented programme.
"For able students, teachers are very willing but they simply aren't qualified in the specific three separate sciences and modern foreign languages, so we have children coming into our master classes who have virtually done no practical science at all, it's all taught practicals if it's done at all.
"It seems to me, if we might really make a breakthrough, we need to train lots of specialist teachers, and perhaps get university dons to come in and help with that specialist science teaching, and modern foreign language teaching in secondaries, particularly in inner city schools."
Speaking after the event, Mr Levin said he did not think universities were producing enough graduates in science and languages, and those that do graduate in these areas are snapped up by top city and accountancy firms.
He said that independent schools have the resources to pay teachers more, and they still find it difficult to recruit top graduates.
Mr Levin said that part of the problem is that students do not do enough science experiments and instead have "taught practicals" which means the teacher does the experiment in front of the class, or they look at it in a textbook.
"They have taught practicals which is a contradiction in terms," he said
"In physics, in chemistry, in some cases children have never really switched on a Bunsen burner."
This means that students are less inclined to study science, he said, adding that because they are not taught by specialist teachers they become "handicapped in terms of competing for Russell Group places".
Russell Group universities, which include Oxford and Cambridge, are considered among the best in the UK.