The Government has created a "crisis" in school places, Labour has claimed after publishing statistics showing more than 80% of free schools did not fill every desk.
Shadow education secretary Tristram Hunt said freedom of information requests revealed free schools had a fraction of the pupil numbers they had planned for because they opened in areas where there were already enough places.
He claimed the scheme ignored areas where there was pressure on places.
Mr Hunt said: "David Cameron has created a crisis in school places, diverting millions away from children in areas with a shortage of school places in order to open pet project free schools in areas where there are already enough places.
"This is affecting standards in schools, with class sizes soaring, pupils being taught in makeshift temporary classrooms, and children having to travel further and further to get to school.
"Unlike David Cameron, Labour has the right priorities for driving up school standards. We will prioritise new school places in areas where there are shortages, have rigorous local oversight of schools and ensure that all teachers have or are working towards qualified teacher status."
Labour's research found seven mainstream secondary free schools were full on opening, and only two mainstream primaries.
The Opposition highlighted the Discovery School in Newcastle, which opened with only a third of its planned pupil numbers, and the Harris Academy in Tottenham, which opened with 58 pupils when it planned for 240.
It said the Trinity Academy in Lambeth opened with 15 pupils when it had planned to admit 120.
Overall, Labour said that of the 69 free schools that answered the freedom of information request, there were 2,564 unfilled places at the start of this school year.
Free schools are funded by central government and independent of the local council in their area. The schools can be set up on a non-profit basis by parents and teachers or groups such as charities, universities, faith groups or businesses.