I found four possible Abram Rubinsztajn born between the years 1926 and 1932.
1.) Abram Majer Rubinsztajn born 14/01/1927 and he lived Hohens 78 Flat 19 and Hohens 84 19. He had a ghetto note with ZAM 25.12.41. He aslo appears as Abram Majer Rubinsztein and he lived at KOPERNIKA 16.
2.) Abram Rubinsztajn born 1929 and Altermieter and Pfeffer 20 14. He was deported on TR 2 on 25/03/1942.
3.) Abram Rubinsztajn born 31/08/1931 and he lived at Hamburger 41 flat 6 and Lipowa 44. He had a ghetto note with 20.12.1943 and he also apears again with the last name Rubinsztein and is living at Hambuger 18 flat 1.
4.) Abram Rubinsztien born 1931 and he lived at Gnesen 13 flat 1 and had a ghetto note of Glucka 4 AUSG.
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There was also a Abram Mordcha Rubinstien born 1933. I wasnt sure if he would have been old enough to attended the school or not.