English boys in the 1930s mostly wore shorts with socks up to their knees a shirt and tie and on top they wore a thick school blazer and cap. They wore these clothes both at school and home, often throughout the winter. Almost all schools required uniforms with shorts, sometimes even for the younger boys at secondary schools. Boys often wore suit jackets or blazers for everyday wear.
However at some schools boys wore more unusual clothes. Some English boys after reaching 13 years of age and sent off to their public schools and wore the basic Eton suit with a stiff collar.
In the book Boy it gives a good description of Roald Dahl's experiences
It was Baden Powell who first introduced shorts when he started scouts in 1908, In the 1930s Lord Baden Powell's introduction of shorts continued.
My Grampa was born in 1924 he wore blazer shirt and tie. He wore long trousers when he was 14. He says all boys went into longs at 14. He says this is when the voice breaks!
