On 20 July 1927, the new school was formally opened by the Lord Mayor of London, Sir Rowland Blades, and was occupied from the following term. The teaching staff was augmented by two in the new school that September. The furniture and fittings cost £3,057, which the Authority took on loan.

Midgley caused a major upheaval in August 1927. When the Education Committee examined the lists of new entrants to the school who had been chosen by him and the staff, they found that 23 boys from the 81 who had been notified by the school of places were from outside Walthamstow, principally from Chingford, where there was no grammar school until 1938. There ensued a correspondence between the Walthamstow Committee and the Essex authority, in which it was eventually decided to allow those who had been admitted to remain. After this, there was rather more supervision of the selection procedure, and non-Walthamstow boys were not admitted in any numbers for another five years.

The school buildings were incomplete at the time of their opening, and the gym/dining hall block was not completed until the 1931/32 school year. This is the very high building which closes the "E" of the main buildings, and became known as the "Bastille". It cost a further £7,000.

In June 1931 Harold Midgley suddenly died, and once more, Arthur Prowse became acting Headmaster. To replace Midgley, the Education Committee appointed Percy Denis Goodall, previously Head Master of Falmouth Grammar School. One gets the impression that under Midgley the school's policy was one of results through solid, conventional, teaching - which undoubtedly paid dividends. Goodall, however, was something of an innovator. He had high ideals on the place of the school in civic and social life, and of education as a means to promoting good world citizenship.

Administrative changes also occurred. In 1932, primary control of the school passed from the Walthamstow to the Essex authority. The demand for places consequently increased. Indeed, the population of the whole south-west Essex area increased rapidly, and the Authority began building a new school at Buckhurst Hill to relieve the pressure on Monoux. But in 1934 and 1935 the school had to expand to four-form entry (128 per year) to cater for the pressure. This put considerable stress on the available resources. In 1933 the system of 100 % special places was adopted, and with it the 11+ Entrance Examination. The system meant that parents paid a proportion of the full fee (£21 per annum for Essex residents) according to their means. In 1935, 45% of the boys paid no fee at all, 23% paid reduced fees, and 2% the full charge. The last vestiges of fee paying disappeared after the passing of the 1944 Education Act. From the 1930s, the "Monoux family" idea was encouraged. The Parents' Association was formed and fostered, the Old Monovians drawn closer into school life. More important, perhaps, clubs, societies and school visits were encouraged on a scale not before known, and the school's corporate identity was established.

The Board of Education again inspected the school in March 1935, and reported in generally favourable terms, with one or two important reservations. Of these, the most important was the lack of an stablished sixth-form tradition. Only 25 boys from 525 were in the sixth, and even that number was on the decrease. An average of 8 boys per year took Higher School Certificate, and 4 went to a University. This no doubt was partly due to the recession in the country at large, and the wish of parents to find their sons secure posts at the first practicable opportunity, but it did little to foster high academic aims for the school. The Inspectors reported also on the scant usage of the new dining room, and suggested it be converted to a biology laboratory. This was eventually done. A certain degree of criticism was levelled at the unimaginative nature of the teaching, especially of the older members of the staff, but no serious lapses were detected. Praise was given in particular to the history and German teaching, to the standard of oral expression in the school, to discipline, and to the prefectoral system.

Later in the 1930s, the teaching of Esperanto was started, reflecting the internationalist ideas of the Head. Another innovation was that of ju-jitsu, for which the school featured in a Movietone cinema newsreel. The late 1930s were also a time of the tremendous dramatic productions - "The Ghost Train" for some reason always occurring to those who remember them. And in the last summer of peace, a fete was held for the Education Assistance Fund, which realised the then huge sum of £600. That same summer, the cloisters around the quadrangle were bricked up at a cost of £904.