This is a common pushback from teachers who are hesitant to make the change to an inquiry driven instructional practice. Considering test prep may be all they have ever known in their educational careers, it would seem like an odd shift to make. It might also come across as scary to many. Andrew Miller, Buck Institute for Education national faculty member, shares this great bit of advice in a recent Edutopia blog post:

Power Standards/Learning Targets

Whether individually or through facilitated professional development, teachers spend a lot of time unpacking the standardized tests and the targeted standards and learning on which they’re based. When you design a PBL project, make sure it hits those frequently targeted standards or learnings. If you know a specific book or genre is a frequent testing target in the AP English Literature exam, use the PBL project to go in-depth on that content. If you know Linear Equations are tested the most often or weighted more in the state test, then use PBL to ensure that students walk away not only knowing their linear equations inside out, but also being able to think critically and make relevant connections.

Be sure to check out the rest of his great post here. There is also another great article he wrote called “Dispelling some misunderstandings about PBL.”