"I believe every girl on the planet deserves the same kind of opportunities that I’ve had," Obama wrote, urging followers to get involved in ensuring educational access for all

Summer is ending, school is starting back and former First Lady Michelle Obama is reflecting on the value of her own education — and what it means that tens of millions of girls around the world still aren’t getting one.

To mark the International Day of Charity on Thursday, Obama, 55, shared a sweet throwback photo on Instagram from her own early school days — complete with bangs and a toothy grin — and encouraged her followers to do the same.

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But she also urged them to go further: “It’s so easy for us to take our education for granted, especially here in the United States,” she wrote along with the photo. “Right now, more than 98 million adolescent girls around the world are not in school.”

She pointed followers to the Girls Opportunity Alliance, run by the eponymous foundation set up her and former President Barack Obama.

“I learned a lot in school—how to do my multiplication tables and structure a paragraph, yes, but also how to push myself, be a good friend, and dust myself off after a failure,” Mrs. Obama, who grew up in Chicago, wrote on Instagram.

Image zoom Former First Lady Michelle Obama’s back-to-school photo Courtesy Michelle Obama

Image zoom Michelle Obama visiting the Elizabeth Garrett Anderson Secondary School in London in 2009 Dominic Lipinski/WPA Pool/Getty Images

Image zoom Michelle Obama (center) with a group of students Courtesy Obama Foundation

She added, “I believe every girl on the planet deserves the same kind of opportunities that I’ve had …. Girls who go to school have healthier children, higher salaries, lower poverty rates, and they can even help boost their entire nation’s economy.”

“The future of our world is only as bright as our girls,” she wrote.

Since leaving the White House in early 2017, Mrs. Obama has continued to focus on the issues she championed while she was first lady, including healthy living and educational access.

She also embarked on a blockbuster international book tour in promotion of her bestselling memoir, Becoming, published last fall.

In a Mother’s Day essay for PEOPLE this spring, she looked back the support she received from her own mom, Marian Robinson, and looked forward to raising the next generation of women.