▶ Watch Video: Handcuffs in Hallways: Hundreds of elementary students arrested at U.S. schools

To many people, it’s unthinkable: Children, some as young as second grade, handcuffed at school like criminals. Yet it’s a reality at schools across the country.

Those types of incidents often make headlines, but the CBS News investigative team wanted to know if there were other cases that didn’t receive public attention.

Where is this data from?

To answer that question, we turned to the U.S. Department of Education’s Civil Rights Data Collection (CRDC).

The biennial survey of nearly every school in the U.S. includes data on everything from test scores to staffing levels to bullying. It also includes data on “school-related arrests.”

This data is from the 2017-2018 school year, which is the most recent available. We’re told by the Department of Education that more recent data won’t be released until 2023.

Want to learn more? We’ve published our code and data for this entire project.

How do we know this is accurate?

We undertook a rigorous data cleaning and verification process, which included contacting individual school districts and state education departments to verify their data.

If we weren’t confident about a school’s numbers, we removed that school from the analysis and took steps to ensure other schools with similar issues were also removed. If a school told us that its data was inaccurate, we followed up, asking for an explanation of what went wrong and how it would be fixed in the future.

We also removed schools that might throw off the data analysis — those inside long-term secure juvenile justice facilities, for example — and those whose data we knew was inaccurate such as online-only schools.

700 arrests sounds low. Are you sure that’s correct?

There are several issues with this data that mean the numbers of arrests of young children in school could be higher than reported.

Several school districts — including Chicago Public Schools and New York City Public Schools — did not report arrest data to the CRDC that year.

Other school districts told us their data was inaccurate. Several schools in Texas, for example, told us they made errors in their CRDC submission because the person filling out the survey misunderstood the questionnaire. Because those schools and others like them were removed, it’s likely the real number of arrests is higher.

Do these include arrest of people who weren’t students but were arrested at schools?

No. The CRDC defines a “school-related arrest” as “an arrest of a student for any activity conducted on school grounds, during off-campus school activities (including while taking school transportation), or due to a referral by any school official.”