Select the best crystal as your 'seed' for growing a large crystal.
All containers must be clearly labelled. Provide the reagents in ready-measured quantities to reduce waste and assist lesson organisation. Heat the copper sulfate solution to evaporate half of the water.
Filter the solution. Most metal oxides are insoluble solids. The blue colour intensifies as more black powder is used. If the acid has not been hot enough, excess acid can co-exist with copper oxide. You don't want 'extra' crystals growing because they will compete with your crystal and will slow its growth.
Copper sulfate crystals. Allow to filter through. The lab would fill with toxic fumes.