I haven’t dug into that data, but it appears to include private spending, and is skewed by higher education. From the same study:

“Several countries outspent the U.S. on elementary and secondary education, including Switzerland, Norway and Luxembourg, which spent $21,595 per full-time student in 2014.

The U.S. also spent less of its total wealth on education than many of its counterparts. In terms of the percentage of the gross domestic product (GDP) spent on education, at 6.2% it trailed Canada, Denmark, Iceland, the Republic of Korea and the United Kingdom.

Most of the money invested in education comes from public sources, both in the U.S. and globally. However, the U.S. invested fewer tax dollars on educating its young people than most countries in 2014, paying 70 cents of each dollar spent on education, down two cents from a decade earlier. The average country in the OECD contributed 84 cents to each student’s bill.”

I’ll also add this, from a just-published report by the Alliance to Reclaim Our Schools (AROS):

“Between 2005 and 2017, the federal government neglected to spend $580 billion it was supposed to on students from poor families and students with disabilities.”

Of course, spending more money alone isn’t the answer. It’s more money + democracy (the more direct, the better). Hence why empowering teachers to collectively bargain for not only themselves but also their students is so important, and why market-based “solutions” like charter schools are a superficial answer.