The first compositions that Klein composed in Terezín reflect the ban on using instruments. This prohibition was turned into a virtue, resulting in a preponderance of amateur choral music, often, though by no means exclusively, organised and conducted by Rafael Schächter, who saw in him an ideal partner with whom he could encourage fellow prisoners to take part in communal singing. Thus, when Klein started to write his first Terezín compositions in the spring of 1942, they were, not surprisingly, choral works, and he did not turn his attention to instrumental music until the following year. Expediency compelled the first choral activities in the ghetto to be segregated between men and women. Because Aufbaukommando deportees were men, the first choral groups, in the early days of the ghetto, tended to be male, though the separation of the sexes, and lack of rehearsal space for larger mixed choirs, were further reasons for segregation.

Klein's first choral works, dating from early April 1942, are arrangements for four-part male chorus of well-known Czech and Slovakian folksongs. The first version of Už mnĕ konĕ vyvádĕjí (‘They are taking out my horses’) is dated 8 April 1942, with Aby nás Pán Bůh miloval (‘If only God would love us’), Na tých naších lukách (‘On our meadows’), Chodíme, Chodíme (‘Walking, walking’) and Chodzila liška (‘A fox walked in’) all belonging to this period. An arrangement of the then-popular 1933 Red Army Poljuško, pole (‘Song of the Plains’), originally composed by Lev Knipper, with lyrics by Viktor Gusev, is dated 20 April. In July, Klein made a second arrangement of They are taking out my horses. It can be assumed that these choral arrangements were performed a number of times. Schächter had determination and vision, as well as immense talent as a choral conductor. His fellow prisoners were, as Lisa said, ‘very hard working men, but he managed to get them to make music. They were so enthusiastic about the music, because he was himself’.

These are Klein's first compositions conceived specifically for amateurs. There was hardly any manuscript paper in the camp at that time, and so he drew the staves himself and, as the folksong settings are not especially demanding for either performer or listener, these adaptations would have been taught by rote. ‘This is how some life started pulsing there’, Lisa explained.