That was part of the British emancipation plan and of the southern plan except for the citizenship part. The British plan called for the training of the younger more adaptable slaves in a trade whereby they could earn a living in open society. While the older slaves would remain as wards of the slave owners or could be freed if they posed no burden upon society.
This was essentially what happend with the slaves in Brazil in 1880's
That sounds like assimilation to me as much as the American society allowed at that period of our history. It certainly was more of an assimulation plan than was offered to the American Indians.