The history of learning how to perform one's duties in the Royal Navy can be broadly separated into 'training' and 'education', and trainee type: ratings, artificers, officers, and the children of RN personnel attending Royal Naval Schools overseas.

The origins of the Instructor Officer (IO) Specialisation date back to 1702 and lie within two separate teaching/training branches, known as 'schoolmasters' and 'instructors'.

A key development occurred in 1918 by Order in Council as follows: Chief Naval Instructor became Instructor Captain; Naval Instructor of 15 years' seniority became Instructor Commander; Naval Instructor of eight years' seniority became Instructor Lieutenant Commander; Naval Instructor of six years' seniority became Instructor Lieutenant.

To distinguish different branches from the General List (GL) of Executive Officers, who had no coloured cloth between their stripes, various colours had been introduced after 1863: Surgeons (scarlet); Instructors (light blue); Paymasters (white); Ordnance (blue); Engineers (purple); Electrical (green). The Royal Navy finally abolished coloured stripes in May 1955, except for those who needed to be clearly recognisable as non-combatant under the Geneva Convention. These included medical and dental officers and civilian officers required to wear uniform.

The instructor and schoolmaster branches were amalgamated in 1946 to form the Instructor Officer (IO) Specialisation, and were thence known as 'Schoolies'. They would go on to undertake a wide range of specialist appointments in Meteorology and Oceanography (METOC), Education and Resettlement, Information Systems (IS), Management Training, and many other areas. IOs joined the specialisation via multiple pathways but Britannia Royal Naval College (BRNC) Dartmouth, Royal Naval College (RNC) Greenwich, HMS Drake and HMS Victory were the most common entry establishments during the nineteenth and twentieth centuries.

The education for IOs varied over time but included parade drills, leadership, basic seamanship, navigation, Morse code, naval history, service writing and wardroom etiquette. Specialist teacher training covered speaking in public and instructional techniques.

Initial seniority depended on qualifications on entry; a good honours degree (1st or 2-1) earned four years seniority in the rank of Lieutenant, a 2-2 or lower degree would gain direct entry as a Lieutenant, with a teacher training certificate (Cert Ed) being the minimum qualification to enter as a Sub-Lieutenant. Past teaching or equivalent experience in years also added to seniority up to a maximum of four years as a Lieutenant.