This particular belief that Indians could gain a dominion status in the 30's itself rests upon two explanations. The first one is eloquently described by one of Gandhi's most trusted compadre, Maulana Azad himself. When Prince of Wales visited India in 1921 and the Congress decided to boycott his tour, every senior politicians were put to jail. This was then, Lord Reading agreed to hold a round table conference with Congress to reach a settlement provided Congress withdraws it's program to boycott Prince's visit.
Each and every senior political leader including C R Das considered this proposal a great opportunity.But Gandhi rejected this offer and demanded unconditional release of every leader, especially Ali brothers. Soon after, the round table proposal was dropped by the Viceroy.To every one's surprise, Gandhiji himself made a similar proposal for round table conference few months later on similar terms. But unfortunately, Prince left India already and the British ha no further interest in this proposal. C R Das termed this incident as Gandhi's great political blunder.
Second explanation and perhaps more plausible and widely accepted one was Gandhi's untimely retraction from non-cooperation movement.It was this time when Michael Collins, though controversially accepted a dominion status of the Irish Free State under the British and provided a rather ideological model for India to have a similar sort of mechanism for itself. The British retreated in Ireland. They neglected Collins' terrorist activities and negotiated with him. Same was the condition in India. If Gandhi held his nerve a little longer, the British would have bowed down to this monumental pressure. The Governor of Bombay, Sir George Lloyd then said," Gandhi's was the most colossal experiment in world history, and it came within an inch of succeeding."
The reason behind the failure of second round table conference is a separate chapter in Indian History and unfortunately it was another saga of a series of errors from Gandhi which we can discuss later. An wise man a great politician of this subcontinent,though in a different context later said,"..but in politics one has to play one's game as on a chessboard." Sadly, Gandhiji did not believe in this rule. His rules of politics were different, inappropriate to be more accurate. If he had waited for the right moment to show his cards, India could achieve dominion status if not complete Independence before 30's quite smoothly.