Mass and weight
Use a balance scale or weight comparison to determine whether a story object is heavier, lighter, or equal to a target measure.
Surface
Mass and weight uses short visual tasks with clear answer actions and repairable mistakes.
Selection
Fresh independent work can move toward Core, Transfer, or Challenge routes; help use or confusion keeps support visible.
Help
Hints keep attention on the visible structure; reveals show the path without counting as independent evidence.
Presentation
Presentation can reduce reading and interaction load without changing the selected skill. Practice focus can bias compatible work without breaking prerequisites or story fit.