When contacted, Smith admitted the words had been taken from Obama, along with "extracts" from other motivational speeches delivered by Ronald Reagan, Margaret Thatcher and a "few lines" from Oscar Wilde.
Next time he would credit the source, he said.
"I took four extracts from four different people. It was the best out of all four. The idea was to make a motivational speech, and I picked the best you can find in the world," Smith said.
He has since altered his public post to acknowledge the world leaders.
"It hadn't occurred to me that it would be important (to say) where the extracts come from.
The eight-minute speech encourages children to show up to school, pay attention to teachers and put in the hard work it takes to succeed.
Smith said he believed the speech had resonated with the 32 pupils at Kumara.
"It's hard to keep young ones' attention but they hung on every word."
