1919-1932
Elementary (Primary) School:
Class 1 - age 7
Class 2 - age 8
Class 3 - age 9
Class 4 - age 10 - upon completion, student could take exam to enter secondary school after 4 years of primary school
Class 5 - age 11
Class 6 - age 12
Class 7 - age 13
Gymnazium (Secondary) School:
Class 1 (junior) - age 11
Class 2 (junior) - age 12
Class 3 (junior) - age 13
Class 4 (senior) - age 14
Class 5 (senior) - age 15
Class 6 (senior) - age 16
Class 7 (senior) - age 17
Class 8 (senior) - age 18 (Matura examination upon completion to enter university)
1932 and onward
Elementary (Primary) school - 7 years (exam can be taken after 6 years to continue to gymnazium)
Gymnazium - 4 years
Lyceum - 2 years (Matura examination upon completion)
https://sztetl.org.pl/en/glossary/education-system-second-polish-republic