While still in elementary school, the educator Rózsa Péter, friend of his mother introduced him to Paul Erdős, who invited him for lunch in a restaurant, and bombarded him with mathematical questions.
Pósa finished the problems sooner than his soup, which impressed Erdős, who himself had been a child prodigy, and who supported young talents with much care and competence.
He went to the first special mathematics class of the country at Fazekas Mihály Secondary School from 1962 to 1966, where his classmates included Miklós Laczkovich, László Lovász, József Pelikán [hu], Zsolt Baranyai, István Berkes, Katalin Vesztergombi, Péter Major.
From 1971 to 1982 he worked at the Department of Mathematical Analysis at ELTE University, and he obtained a doctorate in 1983 with his dissertation about Hamiltonian circuits of random graphs.
At the beginning of the 1970s he got involved with the school reform movement called complex teaching of mathematics led by Tamás Varga.
In a camp, students mostly work in groups of 2-4, but there are also plenary sessions where they discuss solutions, and sum up important thoughts.