Donald Trump's nominee for education secretary has come under scrutiny after failing to answer a basic question on education policy.

Speaking at her Senate confirmation hearing on Tuesday, Republican donor Betsy DeVos was asked to explain her views on how test scores should be used in schools.

The proficiency-versus-growth argument is one that has been widely debated among US policy-makers. Assessing pupils on “proficiency” means to mark them on benchmark grades, whereas judging them by “growth” would be to measure the degree of progress they have made over time.

Answering her interviewer Sen. Al Franken in the live broadcast, Ms DeVos made it clear she was unaware of the difference.

“I think if I am understanding your question correctly around proficiency, I would correlate it to competency and mastery, so each student according to the advancements they are making in each subject area,” she said.

“That’s growth,” Franken replied, “that’s not proficiency”.

By the time Ms DeVos appeared to understand Mr Franken’s question, she had run out of time to answer.

The idea that growth and proficiency are both important tools for assessing of schools’ progress, but that growth is a key factor in determining teaching quality overall, was one that came up frequently in recent debate over rewriting the US law.

At the hearing on Tuesday, Ms DeVos also appeared to struggle when questioned on other Education Department issues including the private schools voucher scheme, student debt and the bedrock federal law guaranteeing an education to students with disabilities.

As education secretary, Ms DeVos would lead the agency responsible for policies affecting public schools, and be in charge of executing Mr Trump's campaign promise to use $20 billion in federal funds to create school choice programmes.