As a sea of colorful streamers and cheering children flooded the new $1.25 million playground at the Rafael Hernandez K-8 Dual Language School in Roxbury last week, a group of former students watched and smiled with pride.

Three years ago, the ninth-graders led the effort to replace their old, broken playground with a colorful, challenging new one, including a ropes course, a paved four-square area and turf-covered green space.

The former students joined Mayor Martin J. Walsh and other officials Thursday to cut a red ribbon on the playground they helped plan, design, and raise money for.

“It all started when a younger student wrote a letter to Principal Ana saying that we needed to redo the schoolyard because it was rundown, dangerous, and in serious need of renovation,’’ a former student Jose Vazquez, Jr. said of the old playground marred by graffiti and broken equipment. “But instead of having someone design the yard, she thought it would be best for [students] to lead this work.’’

They took field trips to view playgrounds at other schools. They interviewed classmates to get ideas, and talked with parents and school staff. They worked with architects and school department officials on the design.

Still, they faced a big hurdle. The price tag for their grand vision was $1.25 million.

But the fund-raisers they organized netted only $60,000.

“We organized dances. We sold food at family events. We went to Lowe’s and applied for their playground grant,’’ Vasquez said. “But, we still didn’t have enough money.’’

So they turned to the one person they thought could help – the mayor of Boston.

“At first, we weren’t sure what the mayor thought,’’ said Lorraine Sanchez, another former student. “We told him that this neighborhood and the children in this neighborhood, and the children in this school deserved better than this. The community deserved an amazing playground.’’

And, after visiting the school and meeting with students who presented their case, Walsh agreed. The mayor’s office funded more than $1 million of the playground as a part of the city’s Imagine Boston initiative.

“When I left here, I just knew in my head – we’ve got to fund this playground,’’ said Walsh during the Thursday ribbon cutting.

“I can honestly say, as mayor of Boston, one of the best things I’ve ever been part of is happening here today at this school.’’

Walsh applauded the ninth-graders for getting the project off the ground. But the students said they did it for the younger kids.

“We wanted to give back to them, even if we weren’t going to get to play on it,’’ said former student Mabel Castillo.

She noted the playground was designed with an eye toward the identity of Hernandez, where students are taught in both English and Spanish.

“We feel like as Latinos, we stand out,’’ Castillo said. “So, since we are bilingual, we wanted the playground to match our school, so we wanted it to have bright colors and to stand out so when you’re driving by it’s like, ‘Oh, wow. Look at that.’ ’’

Boston Superintendent Tommy Chang said he saw the school reflected in the playground, and called the students, “not only the leaders of tomorrow, but leaders of today.’’

“Your voice made this happen,’’ Chang said. “Hernandez is a great reflection of what is possible in schools in Boston. This is a school that affirms the racial, cultural, and linguistic identities of our young people.’’

Laney Ruckstuhl can be reached at laney.ruckstuhl@globe.com. Follow her on Twitter @laneyruckstuhl.