In his first session Frewin studied Second Ordinary Mathematics, Natural Philosophy, and Latin. In his next session, 1921-22, he took Honours courses in Intermediate Mathematics, Intermediate Natural Philosophy, Experimental physics, Heat, Electricity, and Applied Mathematics. After taking Honours courses in Mathematics and Natural Philosophy he gradeuated with an M.A. with First class Honours in his honours subjects in July 1923. He was awarded the Sir David Baxter Scholarship in Mathematics, also in July 1923. It is worth noting that Frewin was in the same class at university as W V D Hodge.
Frewin joined the Edinburgh Mathematical Society in December 1923, immediately following his graduation. At the meeting of the Society on Monday 10 December 1923 the paper The Numerical Evaluation of Double Integrals, by Mr A C Aitken and Mr G L Frewin was read. The paper was published as A C Aitken and G L Frewin, The Numerical Evaluation of Double Integrals, Proc. Edinburgh Math. Soc. 42 (1923). Frewin the went to New College, Oxford where he undertook further study and returned to Edinburgh in 1925 when appointed to George Watson's College, Edinburgh.
After teaching for ten years at George Watson's College, Frewin moved to Inverness. He married Ethel Gillespie and in June 1936 a son was born. The announcement of the birth read:
Article by: J J O'Connor and E F Robertson