The Dennis Memorial Grammar School is one of the achievements of the Christian Missionary Society in Onitsha. The foundation stone was laid by Colonel Moorhouse, C.M.G., D.S.O., Lt. Governor of Southern Nigeria, on February 2, 1923.
The actual building of the school started in 1920. It was formally opened in 1925. Mr. C.A.A. Barnes, a Gold Coast architect and surveyor designed the school building free of charge.
Under the able principalship of Rev. Jones and Rev. C.J Patterson, the school made a name for itself in the field of sports. It also won academic laurels by the unprecedented number of passes of its students in the Cambridge School Certificate Examination.
The first intake consisted of nineteen boarders and forty-six-day students. Most of the students came from Onitsha and the surrounding towns where the missionaries had worked for over half a century and where people had begun to appreciate the economic value ‘of English education.
The curriculum took after that of the average English grammar school of the period and was essentially designed to produce a literary type of education. It was meant to produce an elite that would take to the high professional jobs. It was also meant to produce highly accomplished elites who are expected to perform their professional jobs effectively and also become effective leaders.
The letters D.M.G.S stand for Duty, Magnanimity, Gratitude, and Service. These are some of the abiding values, which D.M.G.S. has always symbolized. These are some of the ideals that will rescue D.M.G.S. in times of strain and stress.
Some notable students of DMGS include Harford Anierobi (retired senior Administrative Officer, Isaac Iweka (the distinguished pioneer Civil Engineer, now the Eze of Obosi), Wilfred Mbanu (retired Rev. Canon bf the Anglican Church) Isaac Nwangwu (retired Civil servant), Alfred Ogbolu (a retired civil servant), Jonathan Ogbonna Ekeocha (a retired educationist) and “Walter Onubogu (a well known medical practitioner).