Let the students play with the toys! I worked for a program called Junior Engineering at Utah State University for over 10 years taking science and engineering modules/equipment to elementary schools around the intermountain west. When the teachers used our materials to let the students play, the lessons became fun!
The program was cut due to funding issues, but we have some fun ideas on the website of the non-profit I'm currently working with
There are some other ideas in the following hub that I posted last year.
Again, let the students play with the equipment!