ABC News

ABC News' Michael Falcone reports:

Since last Wednesday's debate in Arizona, Rick Santorum has been defending his evolving position on President George W. Bush's signature "No Child Left Behind Act."

Santorum did so again on Sunday morning in an interview on ABC's "This Week" with George Stephanopoulos.

"Governor Romney defends No Child Left Behind and supports it today," Santorum said. "I don't, because it's against the principles I believe in.  It's obviously not against the principles that Governor Romney - I have principles.  I have principles that support the basic foundational principles of our country."

As a Pennsylvania senator, Santorum voted for the original bill in 2001. However,  it is unclear exactly when Santorum's reservations about the education law first surfaced.

In fact, four years after the law took effect, he was still  touting "No Child Left Behind" as "the most historic legislative initiative enhancing education opportunities to pass Congress in decades."

That quote comes from an archived version of Santorum's 2006 Senate campaign website.

"Rick Santorum supported the No Child Left Behind (NCLB) Act, which has been the most historic legislative initiative enhancing education opportunities to pass Congress in decades. This legislation sets important standards for our schools, our teachers and our children. By setting high accountability standards, NCLB encourages teachers and schools to excel while also providing the tools to improve performance if changes are needed. Further, NCLB gives teachers and school administrators' flexibility by decreasing bureaucratic red tape that hinders access to grant programs, which allows states and localities to redirect resources directly to the classroom."

On his current presidential campaign website, Santorum said "No Child Left Behind" should have been "initiated at the local level":

"The Truth About 'No Child Left Behind': Parents and citizenry should hold schools accountable and have educational options for their children. Steps were taken in this direction in No Child Left Behind, but it should have been initiated at the local level where the consumers, taxpayers, and children are.  States may choose to adopt common core standards, but they should not be forced on states, private schools, or home schools."