So how should we introduce a problem and then keep pushing our students toward a goal that ensures successful knowledge gain? Here are a couple of videos that let you see teachers discussing their driving questions (notice that these are both at the high school level).
Watch this entire video to see teachers discussing components of the driving question and subsequent questions that will need to be examined.
I love this discussion of crafting a driving question. This link starts in the middle of the discussion but there are some key points made here.
When we are creating a driving question we want to know what our students should be learning and we need to think of questions that must be answered by our students as they demonstrate knowledge. That is rather obvious. But how much do we give to our students, up front, and how much do we expect our students to ask/answer by themselves.
With upper elementary students and lower middle school students we will need to drive them to the questions they need to ask. They may not know what they need to know to be successful. As the students mature we will need to guide their questioning. This is usually expressed as their Knows and Need to Knows. We help them make a list of items they will need to learn.
With our secondary students we may just need to facilitate their discussions of Knows and Need to Knows. They should be able to brainstorm what will need to be learned during the project. And so we are able to guide them to the driving question. They create the question that will drive their learning.
In more advanced (with PBL) classes we can even have our students create their problem statement. The overarching problem can be tackled from many different directions and therefore the students will need to decide how they want to tackle it. They create the problem and the ensuing driving questions.
To sum up these thoughts, I would suggest students who are in their first year with PBL or those students who are at the elementary level will need to have a problem statement and driving question from the outset and generated by the teacher. Middle school students or students with more than a year of PBL should be able to take a problem statement and create the driving question. (Note: at this point groups may have different driving questions. It will be up to the teacher to ensure they are heading in the right direction with their problem.)
Finally, those students with years of PBL experience and a high enough maturity level, will be able to take a "problem" and create a problem statement and their driving question. They should also be able to create sub-questions that will need to be answered for their group to successfully answer their driving question. It is at this point that the teacher truly becomes a facilitator.
Some might look at this as when the teacher's job is done. However, this is when a teacher must be at his or her finest. Teachers must guide the students with their learning which might mean a sudden need for a workshop on a topic, about which, the teacher may only have cursory knowledge. Then the teacher may have to do their own learning on the topic. This is why many teachers describe their experience with pbl as "the most walking I've ever done - I never get to sit!"
Whether you are providing the problem statement and driving question or you are facilitating as groups create their problem statement and driving question(s), you must be tuned in to every discussion and conversation happening in your pbl groups. With advanced work on what you want the problem statement and driving question to be, you will be able to give your students a framework for rich conversations that will foster a deeper understanding of a topic. And, hopefully, those students will be more capable in using the required skills that drive your curriculum.