Community in the Classroom
Community in the Classroom ( http://www.crscience.org/scientists/ ) is a nonprofit whose goal is to introduce kids to all sorts of exciting science, by getting local scientists ( or scientists in training) to go into the classrooms and present an hour worth of a lecture. Besides the bare bones 1 hour lectures, CIC is trying out a new program, Scientist-Teacher partnership where you would be more involved in a working relationsip with a teacher.

Science and Education Partnership
The Science and Education Partnership (SEP) ( http://biochemistry.ucsf.edu/~sep/ ) is run through UCSF. They have a number of programs, but the Student-Teacher Action Teams (STAT) program allows you to connect with an elementary, middle, or high school teacher (together with other volunteers) to plan and teach four science lessons in the classroom in the spring.