It basically acts as a federal lever of legislative control over the individual states' Depts of Ed. According to its wikipedia page (https://en.wikipedia.org/wiki/United_States_Department_of_Ed...), the highlights include:

- regulating how states are accountable for standardized tests (No Child Left Behind, later Every Student Succeeds)

- regulating federal student loans

- civil rights (LGBT, race, etc.)

- federal assistance for low-income students and underperforming schools

They don't dictate curriculum or anything. So basically it falls under the old argument of Federal vs State control over education. Conservatives have been trying to get rid of the Dept of Ed ever since it was made a cabinet-level position in 1979. They might now have their chance.