Years into Common Core learning standards, teachers lament a lack of good teaching materials

It's been five years since the Common Core learning standards began to take hold, but many teachers say they still lack the resources they need to teach them.

A recent report from the Thomas Fordham Institute calls the need for standards-aligned curricula the most cited implementation challenge for states, districts and schools.

Publishing industry executives say some publishers produced materials more quickly than others, but other factors have been at play. Most significant are the lingering effects of the recession, which left many districts without money to replace textbooks published before the new standards took hold.

In the meantime, the so-called OER movement — short for open educational resources — continues to make gains, with anyone from teachers to states making curriculums available for free or for sale online.