Only in 1925, when he entered the Lycee of Krzemieniec, did he learn Polish. Kac studied Latin and Greek at school as well as mathematics, physics and chemistry.
Lamang sa 1925, kapag siya ang pumasok sa Lycee ng Krzemieniec, siya ay matuto ng Polish. Kac-aral ng Latin at Griyego sa paaralan pati na rin ang matematika, pisika at kimika.