I had a girlfriend & her husband who were told their son was a 'bit slow' as he reaction to things were slower than normal or no reaction at all or an over reaction with anger, & his speech wasn't to the 'standard' it should have been. They eventually took him at the age of 9 to another doctor who discovered he was stone deaf. The doctor suggested that he should test their younger daughter, he discovered she was also stone deaf. In their case they simply needed grommets or myringotomy tube inserted into the eardrum in order to keep the middle ear aerated for a prolonged period of time, and to prevent the accumulation of fluid in the middle ear.
Their son's reaction when touched to gain his attention if he wasn't looking directly at them was shock, which made him appear to react with anger if he lashed out at them, as anyone would.. Both their son & daughter had taught themselves to lip read, so there seemed nothing amiss with their daughter at 3.. Once the grommets were inserted they were both normal & could hear perfectly. https://en.wikipedia.org/wiki/Tympanostomy_tube