In this lab, students will need density blocks, a beaker of water, and a balance. First, students will find the mass of five different density blocks. Then from their knowledge of the mass, students will predict if the block is more dense or less dense than the water. Next, students will test the blocks. Finally, students will conclude that (generally speaking) the more mass the block had, the more likely it was to be denser than the water.
I had students complete this with partners or independently, but it also works well as a whole group lesson. In pairs, the mass of each block is found. Then, as a whole class we test density.