11 years and up.
LEGO Chemistry starts with students doing a wet lab. The lab is from the GEMS guide Chemical Reactions, which uses some fairly common materials for some very uncommon reactions. Students work through combinations of all or some of the materials to determine which were responsible for particular reactions. We go over proper lab procedure for a chemistry experiment (although not lab write-up).
We next go over some vocabulary pertinent to chemistry, and chemical reactions. It is at this time that we explain that each LEGO brick represents one atom, and that different-color LEGO bricks represent different elements. We discuss molecules, mixtures, and compounds. Students practice writing chemical formulas (although not equations). Finally, using the LEGO bricks, students will model the original chemical reaction that we worked through.