For both the grade 1 (heat energy) and grade 2 (liquids and solids) Ontario curriculum, here is an observation sheet that incorporates both curriculums. My students LOVED this experiment! You just need a tin of hot chocolate (I gave each group (I had four) 2 tsps per temperature of water), spoons, a timer - I used the same timer for the whole class and they had to drop in the mix at the exact time, ice cubes and 3 mugs per group. A great experiment for a cold, wintry day! You can even incorporate safety into this lesson, in how to handle hot liquids.
Note: For safety reasons, I just used hot tap water instead of boiling water. I also made a separate thermos of hot chocolate pre-made for students to enjoy after the experiment.