U.S. Sen. Michael Bennet of Colorado on Thursday fired back at U.S. Secretary of Education Betsy DeVos for her criticism of Denver Public Schools’ nationally recognized school choice system.

The Democrat took to Twitter to challenge DeVos’s implication that choices in Denver are lacking because students may not use private school vouchers or don’t have enough charter schools from which to choose.

Bennet was superintendent of DPS before being appointed to the Senate in 2009. Under his leadership, the urban school district launched a series of school reforms that remain in place today.

More than a quarter of the district’s schools are charter schools, which receive public tax dollars but are run independently of the school district.

During her confirmation process, Bennet invited DeVos to Denver to see how the city has embraced school choice and innovation.

Earlier this month, DeVos singled out Denver for providing transportation to some students who choose a school within certain regions. But in a speech Wednesday, she chastised the city’s choice polices after its choice system was ranked No. 1 in the nation by the Brookings Institution.

“The benefits of making choices accessible are canceled out when you don’t have a full menu of options,” she said, pointing to New Orleans as a better example of the choice ecosystem she’d like to see. “Choice without accessibility doesn’t matter. Just like accessibility without choices doesn’t matter. Neither scenario ultimately benefits students.”

DPS Superintendent Tom Boasberg also challenged DeVos’s characterization, pointing to the district’s efforts to hold all schools, charter and district-run, to the same enrollment rules and accountability systems.

In a follow-up tweet, Bennet said his invitation for DeVos to visit Denver still stands.