• Quick retrieval from earlier learning (One material, many objects; one object, many materials). Students answer on mini whiteboards.
• Show answers together and note who needs support in the main task.

1. Which of these is usually made of wood? (a window / a bicycle frame / a pencil / a drinking glass) → a pencilPrompt: Think about how each object feels and what it needs to do.
2. Three of these are usually made of metal. Which one is NOT? (a T-shirt / a bicycle frame / a saucepan / a key) → a T-shirtPrompt: Name the usual material of each object.
3. A chair can be made of wood, metal or plastic. Which property must ALL chair materials have? (strong enough to hold a person / see-through / stretchy / soft like a pillow) → strong enough to hold a personPrompt: What is a chair's main job?

• Pass round objects made of different materials and ask why each one was chosen.
• Share the objective: Build, take apart and rebuild with the same pieces. Read the success criteria together.

• Work through the example out loud, saying why you do each step, not just what you do.
• Example: Ben builds a house from 32 building bricks, then takes it apart and uses every brick to build a bridge. How many bricks are in the new model?
• Step 1: The same pieces are just arranged differently.
• Step 2: So the answer is: 32
• Answer: 32
• Pause after each step and ask a student to say what comes next.

• Do these together. Students try each step on whiteboards before you reveal it.
• Use the hints as prompts rather than giving the answer.

1. Diego builds a tower from 28 building bricks, then takes it apart and uses every brick to build a house. How many bricks are in the new model? → 28Prompt: Were any bricks added or lost?
2. A model castle is made of 9 wooden blocks. Each block has a mass of 10 g. The castle is taken apart and rebuilt as a boat with all the same blocks. What is the mass of the boat? → 90 gPrompt: Does changing the shape change how much material there is?

• Students work on the student sheet. Circulate and check the first two answers of every student early.
• Students who finish: write a question of their own for a partner, with the answer.

The 6 questions are on the student sheet below, with answers in the key.

• Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.

1. A model castle is made of 15 wooden blocks. Each block has a mass of 5 g. The castle is taken apart and rebuilt as a boat with all the same blocks. What is the mass of the boat? → 75 gPrompt: Does changing the shape change how much material there is?
2. Why are many toys and buildings made of small pieces joined together? (Small pieces are easy to carry and can make many different shapes. / Big pieces cannot be made. / Small pieces are always stronger than anything else. / Pieces disappear if they are big.) → Small pieces are easy to carry and can make many different shapes.Prompt: Think of bricks in a house or blocks in a toy.

Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-2.