Gender: boy
School:
School #20A
Only one exact result came up in a search for Mendel Mass, and he was born in 1931, which made him the right age to have attended School #20A.
A few people lived at the same (or at least one) address as did Mendel. He lived with his father, Hersz (b. 1888), his mother, Chana (b. 1902), and his sister Dworja (b. 1926).
Chana only lived at the Franz address with the rest of the Masses, and not at the Langemarkt address (she instead lived at an address on Muhl).
While no deportation information or other information regarding fate is given for any of the other members of the Mass family, Mendel was deported on September 10, 1942, on which date there was a deportation to Chelmno.