When explaining about the macromolecules it is a good idea to have students make the models, since modeling is so much a part of the engineering process and NGSS. If you do not have the plastic model balls, you can have each student make their own to keep in an envelope in their notebook for quick reference. Even though the models will be flat, it still helps them to understand molecular models better. All you need are coins and paper! You can save paper by putting the directions up on the ELMO or writing them on the board. They can also be used for quick assessment.