The negatives: separated children from their parents, kinship network and culture for extended periods of time, intentionally effaced native languages and the transmission of native cultural and religious traditions.
The positives: separated children from extremely unsafe environments (childhood mortality rates "back home" exceeded 50%), saved children from native cultures which featured extreme cruelty, slavery and misogyny, introduced children into participation in the wider civilization, made their survival and (arguably) their peoples' survival possible.
So, a mixed bag.
Now it is non-PC to refer to it as anything other than "cultural genocide."
My mother was born in Northern Alberta,during the period of residential schools. She had to walk, one way, 5 miles.
There were few options to help bring natives forward. The only thing I can think that might have helped was putting them in residential schools when they are ten years old and giving a slightly accelerated program to ensure a reasonable timely graduation.