Top state schools are entering their students for A-levels like general studies and critical thinking in order to inflate their results, an education charity has claimed.
The New Schools Network said it had found that the the top 500 state schools for A-level results accounted for nearly 90% of all entries for the two subjects.
But it warned that although general studies and critical thinking carried the same amount of points as all other A-level subjects, Russell Group universities refused to include them in student application offers.
The two subjects attracted 21,321 entries in 2013/14, making general studies the second most popular subject after maths in the top schools.
Only half of all entries in the top 500 state schools were for "facilitating" subjects - those deemed by the Russell Group as the subjects that best prepare students for university study.
In contrast, facilitating subjects made up almost two-thirds (63%) of independent school entries.
Free schools came top of the class, with 70% of entries in facilitating subjects.
Across all state-funded schools, the figure was fewer than half (45%).
Independent schools also attained more A* or A grades at A-level, with almost half (44.6%) of their entries achieving these grades, it said.
But only three in 10 (30%) entries mustered an A or A* in the top state schools.
Entries per pupil were also higher in these schools than independents, suggesting that while state pupils may be entered for more subjects, they are achieving lower grades.
Overall, state schools continue to lag behind the independent sector, performing significantly less well on A-level points per pupil (717.7 to 836.7) and per entry (204.3 to 236).
Nick Timothy, director of New Schools Network, said: "A-level study is for many students the most important part of their academic career, and success is especially crucial today.
"With the lifting of the controls on university student numbers this year, we now have more people than ever competing for university places, with admissions tutors increasingly discerning between subject choice.
"But the New School's Networks findings show that under the surface many of our best state schools are not providing the quality and rigour that students badly need.
"With over half of A-level entries from state schools coming in subjects that the best universities refuse to recognise, and too few pupils getting the top grades, too many are missing out."