Preschools help boost the academic careers of children who have fewer educational experiences at home, a study suggests.
The effect lasts into secondary school with preschoolers from all backgrounds twice as likely to do AS-levels, say the Oxford University researchers.
The advantage was more than just an early grasp of numbers and letters.
"High quality early education makes the child a more effective learner," said co-author Prof Kathy Sylva.
Activities such as singing songs and nursery rhymes, teaching and playing with numbers and letters, reading with their children and taking them to the library "turn the child on to learning", said Prof Sylva, professor of educational psychology at the university's department of education.
The researchers tracked the education records of a nationally representative sample of children who were attending 141 preschools across England in 1997 and compared these with those of a sample of children who had minimal or no preschool experience.
The study, published by the Department for Education, found parents who provided their children with "stimulating learning experiences" as toddlers, gave them a big educational advantage throughout school.
Children who had this early support from parents were also more likely to go on to achieve better A-level grades, say the researchers - but preschools can help offset this early advantage, the study found.
Preschools whose support was rated "highly effective" in teaching early number concepts saw their pupils four times more likely to do well throughout school.
"Our findings reveal that preschool boosts a child's chances of doing well at school and going onto to take A-level examinations," said principal investigator Prof Pamela Sammons.
"Our research also shows that a child's educational experiences at home when they are under five really matter to their later academic success.
"Unfortunately, not all children get the same support from their parents and for these pupils, preschool is especially important."
Prof Sammons said the findings proved investment in preschools paid off and had particular benefits for children from disadvantaged backgrounds.