I first fell in love with problem-based learning (which I will refer to as "PBL" from here on) in 1998. In fact, this was my first extensive experience with ASCD, having been sent by my principal to a 3-day workshop in Seattle. (My notes are here.) At the time I knew nothing about it PBL...and by the end I felt somewhat evangelical. Over the years, I've tried a number of PBL units with kids with varying success. There are a few key elements that have to be in place for things to work.
The prompt (problem) must be finely tuned. Students must be placed in a position of someone who has the power to make decisions about a real-world problem. PBL purists will tell you that all students need to take on the same role. This does not mean that they will all have the same opinion about the problem or come up with the same solution, but it will help the inquiry and discussion along when they have the same mindset. Secondly, the "hook" that drives the inquiry must be irresistible to students. And finally, the problem must be "fuzzy" or "sticky"---there is not just one right answer. Here is one example of a possible prompt:
You are participating in a toy car race. You have two different cars and need to decide which one you want to use for the race. One car is very light, weighing very little. The other is very heavy, weighing much more. You will conduct an investigation rolling two different balls representing your cars down an incline ramp. From this investigation you will collect your data using digital applications (Excel spreadsheet, PowerPoint, etc.) and use that data to create a line graph representing the speed of each ball. From these results you will make an informed decision on whether the lighter or heavier car would be more likely to win the race.It's not too bad. Some kids would no doubt enjoy participating in a toy car race, such as the pinewood derby's run by the Boy Scouts. This prompt does ask students to make a decision, but note the perspective: they are only making a decision for themselves. This is not a powerful role.
So what if we twist this a little:
You have been asked to judge a toy car race. Last year, some cars were so much faster than others that it was believed some racers might have cheated. The organizers want the race to be fair. They would like you to write a set of at least four rules for the event to ensure no car can cheat to win. The rules must be based on evidence about how weight, time, and distance affect the speed of an object rolling down a ramp.Ah, now the student has some power---s/he is the judge. And, we have a problem to solve---we don't want any cheating. What will it take to make the race fair? Now students have a reason to build their background knowledge with the relationship between weight, time, and distance. We have a hook.
To develop the rules, you will need to plan and conduct an investigation, collect and interpret data, and explain how your rules will make the race fair. Use digital tools to organize your information and communicate your results to the Racing Committee.
Next, the teacher must present it as a real problem. This does take a bit of suspension of disbelief on the part of the students, but if you've built the prompt well, they will have no issues. A first grader will believe that the school nurse is asking them for advice. A tenth-grader will buy in to the idea that they are genetic counselors advising a real couple. It's hard to explain, but kids need a sense of hope that they really are being asked something significant. If students ask you if the problem is "real," just ask them if it matters. Most want to enjoy the Santa Claus/Tooth Fairy/Easter Bunny effect. Let them have the illusion.
Finally, PBL is about cognitive demand---it requires deep thinking about content. Students have to understand a variety of concepts and put then put them together. Understanding enough about how weight, time, and distance affect objects rolling down a ramp so that you can create rules is much more difficult than simply choosing between a heavier/lighter car.
Project-based learning units have different qualities. First of all, they might put the student in a position to act, but only from a kid-based viewpoint. There's nothing wrong with this---influencing change (especially social change) is important regardless of one's age, but it is not the same as being the one who gets to make the decisions. Project-based learning tends to have more visible results and more community connections than PBL, however. In that sense, project-based learning could be considered as more rooted in the real world. Finally, project-based learning is more focused on collaborative outcomes and action.
Each of these units can have a place in the classroom, but it is important to remember that they aren't interchangeable terms. Mind your p's.