Mariana Garcia's blog has wonderful PBL resources. This post has projects for life science, earth science, physical science, engineering, and STEM competitions.
I often times learn from examples. This is an example I found during a research project. It provides an example of a PBL unit and how it changed the student's attitude toward science.
A Gardener's Dilemma Project Idea: Students act as community members and set aside plots of land for local citizens to establish small gardens.Students will design a plan for a family garden plot. I will adapt this PBL to include technology, ELA, Science and of course, Mathematics for elementary students. I like that it is a real-world skill, affecting everyone and involves community planning.
Science Technology Engineering Mathematics (STEM) Education - Over 1000 STEM Curriculum based connections with video, lesson plans, and more for k-12 schools. This page features: App Developer: Athletics And Body Systems ( Grade 7 )