Stearn was largely self-educated and his widowed mother worked hard to support him while at school but could not afford a university education for him, there being no grants available then. When not at the Botany School, he attended evening classes to develop linguistic and bibliographic skills. His classes there included German and the classics. He obtained his first employment at the age of 18 in 1929, a time of high unemployment, to support himself and his family. He worked as an apprentice antiquarian bookseller and cataloguer in the second-hand section at Bowes & Bowes bookshop, 1 Trinity Street (now Cambridge University Press), between 1929 and 1933 where he was able to pursue his passion for bibliography. During his employment there, he spent much of his lunchtimes, evenings and weekends, at the Botany School and Botanic Garden. This was at a time when botany was thriving at Cambridge under the leadership of Seward and Humphrey Gilbert-Carter.