I can't remember to whom it is attributed, but I heard a great quote recently. "The only teachers are models and reflection." This quote gave voice to my convictions about PBL education. Everything I ask students to do needs a model, and an effective way to measure their growth is through their reflection.
In terms of social emotional learning, reflection is useful for building a sense of self-awareness too. Leading students to be reflective and examine their work and motivations helps to foster presence of mind in the future. Reflection can become a frequent act, occurring throughout a project or experience, until it becomes something like consciousness and presence of mind.
Honestly this is a goal for myself. Last semester while working through student reflections, I commented to a colleague that the students were more reflective that I had been in college, and that I hadn't been reflective at all during high school. "I just wasn't a reflective person in high school" I said.
"That's because nobody asked you to be" they replied.
Philip Estrada is a teacher at High Tech High Media Arts in San Diego California. He teaches Physics by having kids build things in a woodshop.