The Archbishop of Gdańsk, Tadeusz Wojda, called the incident a scandal.
"Every insult to the cross violates the religious sentiments of the faithful and provokes justified concern and resistance among people of good will," Wojda explained Wednesday.
According to the archdiocese, the incident took place at the beginning of the week at an elementary school in Kielno in the municipality of Szemud in the north of Poland.
Parents reacted with outrage and criticism.
The case spread via social media.
The archbishop called for reflection, mutual respect and a quick reappraisal.
"Given the current situation, I expect the school management and the school board to provide a thorough and comprehensive investigation into the incident, as well as concrete measures to prevent similar incidents in the future," Wojda said.
At the same time, he thanked all those who had attended and prayed at a atonement service in the parish of Kielno as an act of reparation.