He spent 54 days in space, commanding the last flight of the Space Shuttle Endeavour in 2011. His identical twin brother returned to Earth in early 2016 after nearly a year on the International Space Station.

You would think that brothers Mark and Scott Kelly were always destined for the stars.

But when Mark Kelly returned May 19 to his New Jersey primary school (renamed the Kelly Elementary School), he said he wasn’t always such a great student, or even much of a pilot.

He recalled his instructor telling him after his first landing on an aircraft carrier: “You’re not very good at this. Are you sure this career is for you?”

The experience pushed him to keep trying, he told students, and he eventually overcame what he described as “a serious lack of aptitude.”

“The guys that did really well that day didn’t go on to become test pilots or astronauts,” he said. “But the guy that really struggled that day — me — did. How good you are at the beginning of anything you try is not a good indicator of how good you can become.”

Mark Kelly participated in a yearlong “twin study” while his brother was in space to study the human body’s response to lengthy spaceflights. Their work is helping scientists prepare for future missions to Mars.

Primary schoolers interested in going to space? You’ve got time — keep trying.

Future astronauts

Two boys in red baseball uniforms standing in front of crowd (NASA)
Future astronauts Mark Kelly (left) and his brother, Scott, play baseball in 1971. (NASA)

Back to school

Scott Kelly and Mark Kelly speaking at lectern (© AP Images)
Retired astronaut Mark Kelly (left) listens as his twin brother, Scott, speaks at a renaming ceremony for the twins’ primary school in New Jersey. (© AP Images)

This article draws on reports from the Associated Press.