Both Mr Sandmann and the Native American man, Nathan Phillips, say they were trying to defuse tensions that were rising among three protest groups. Phillips was in the middle of a ceremony for fallen soldiers, all while the students tried to yell over and belittle him and fellow protesters.
The students, who attend Covington Catholic High School in Kentucky, began jeering at Phillips as he took his drum and began singing. And yet, he persisted.
And now almost four years later, the students making fun of Phillips were in Washington D.C. for a pro-life rally when they encountered him. While there, the students evidently made a decision to crash the Indigenous Peoples March as well. A snippet of video from the apparent confrontation quickly gained traction on social media, with many condemning the students - some of whom were wearing "Make America Great Again" apparel - and some calling for them to be identified and harassed.
The Native American, Nathan Phillips, told The Associated Press he approached the Kentucky students to keep the peace between them and the third group of protesters.
Philips gives a very different account of the confrontation, saying the teens were chanting "build the wall" and that Sandmann blocked his path. "This behavior is opposed to the Church's teachings on the dignity and respect of the human person", the officials said.
The videos show members of the Indigenous People's March, one playing a hand drum, surrounded by others wearing "Make America Great Again" hats and clothing. Schilling, who is a member of the Mohawk tribe, said Phillips was pelted with trash just a few years ago by Eastern Michigan University students who hosted a Native American-themed party. "They are all positive in nature and sound like what you would hear at any high school", Sandmann said in a statement, adding at no point did he hear any students chanting "build that wall" or anything "hateful".
'The matter is being investigated and we will take appropriate action, up to and including expulsion'.
"Before anybody else came here we never had walls, we never had a prison".
"It was getting ugly, and I was thinking: 'I've got to find myself an exit out of this situation and finish my song at the Lincoln Memorial, '" Phillips told the paper.
"They went from mocking us and laughing at us to singing with us".
Congresswoman Deb Haaland, one of the first Native American women to be elected to Congress, tweeted that the students showed "blatant hate, disrespect, and intolerance". "I pray for you", she wrote.
"When we arrived, we noticed four African American protesters who were also on the steps of the Lincoln Memorial", Sandmann's statement said.