Gender: boy
School:
School #20B
A search for J* Korenblum turned up a direct match, Josef Korenblum, who was born in 1930--this made him the right age to attend School #20B.
Josef lived with his father (Lejbus, b. 1902), mother (b. 1899), and siblings Rysa (b. 1929) and Ruchla (b. 1933). All the members of the family were deported on transport 37 on March 25, 1942, during the month of daily deportations to Chelmno.