I had a look into school records but unfortunately it seems that the local record office doesn't hold them. Not sure where they would be now after over 100 years!
Sorry, I neglected to mention that there was another sister, Ann, who had married well before John was born. So I think the question is regarding why Ann didn't raise the baby (or their mother)? Why would Amelia have stepped forward if she wasn't the actual mother?
One thing regarding Amela's husband - he is not to be found in the local area in the census before John is born. The closest I can find is that he is at an army barracks. This could make sense because I know his brother was also in the army at this time and actually died in South Africa during the Boer War. So I guess that could explain why his marriage to Amelia was delayed after John's birth. Maybe he was away in the army at the time?
So many questions and possibilities!