When Fenner was appointed, regret was expressed that no South Australian was considered suitable for the job. Although theoretically in an ideal position to influence the department's activities, he was frustrated by having to work within a pre-established framework, by the financial constraints of a world war and the Depression, by political procrastination, by opposition to his proposed reforms and by ill health. His plans for a unified technical education system were undermined by the autonomous South Australian School of Mines and Industries and by delays, until 1940, in expanding secondary technical education on the model of Thebarton Technical High School (opened 1924).

Fenner encouraged innovation, an example being an individual freedom scheme of learning introduced in 1927 at Thebarton, details of which are outlined in a paper by Fenner and Paull (1930), which was read before the Education Section of the Australasian Association for the Advancement of Science in Brisbane. Fenner's criticisms of traditional schooling, summarized in his first essay after appointment as Director of Education (Fenner, 1940), were influential in liberalizing the primary school curriculum. He supported the teaching of technical subjects in high schools and liberal subjects in technical schools. He established a vocational guidance and placement scheme and argued for raising the school age. He was also responsible for technical training courses for unemployed youths during the Depression and for reconstruction schemes for troops returning from both world wars. He helped draft the 1917 Technical Education for Apprentices Act which, with its concept for compulsory, part-time, technical study for apprentices, set a precedent for other States.

Fenner was a figure of his time in stressing the views of education for citizenship and technical education as a means of providing skilled labour to develop South Australia's industrial base. In other respects he was forward thinking: his proposals and educational articles were based on research on overseas and interstate trends, appraised in the light of local needs and conditions…His Directorship coincided with World War II. This exacerbated Fenner's impatience at being unable to effect changes that he had advocated for two decades; he increasingly sought refuge in writing. Overall, local prejudice no doubt contributed both to the difficulty in having his ideas accepted and to Adey's appointment to the Directorship in 1929, despite Fenner's broader and longer experience of high-level administration and his superior intellectual standing.