Presentation: Algorithm for a Stage Change

Slide 1 of 7 · Settling starter · Drama · Year 8

3 minutes

Algorithm for a stage change: 4 crew, 90 seconds of blackout

You have a worksheet with a brief, 2 set lists and the rules. Scene 1 is Nan’s kitchen, Scene 2 is a hospital waiting room, and the blackout between them is 90 seconds. Today you write the algorithm for 4 crew to strike the kitchen and set the waiting room, then a partner runs it step by step to see if it breaks.

While the register is called: write your name, class and date on your worksheet, then read The brief and its 4 rules.

Starter question: Which rule means the vending-machine flat cannot come on straight away?

DCF: Data and computational thinking → Problem-solving and modelling No computers needed · pencil and rubber, the timings get redrafted

Supply teacher script (no subject knowledge needed)

Hand out: one worksheet per pupil, pencils and rubbers. No computers and no stage are needed; this is arithmetic and logic done with a pen. Pupils work alone for the planning and in pairs for the dry run at the end.

Say aloud: “Name, class and date at the top. While I take the register, read the brief and the 4 rules underneath it. Find the rule that stops the vending-machine flat going on first.”

Starter answer: rule 4, nothing can be set in a position until whatever was there has been struck. The flat goes where the kitchen table was, so the table (12 seconds, 2 people) must be off first. The other rules: no more than 2 people in the upstage doorway at once; struck items go off through the upstage door or stage-right wing, set items come on from stage left; the table and the flat each need 2 people.

Slide 2 of 7 · Today’s brief and key words · Drama · Year 8

3 minutes

Your brief: work out what depends on what, run jobs in parallel, test it

A scene change is an algorithm: instructions, in order, carried out by 4 people at once, that must finish inside a fixed time. You will circle the 2-person jobs, work out the dependencies, fill the timing table with a column per crew member, write an IF for the table legs and a REPEAT for the chairs, then swap and dry-run a partner’s plan.

Dependency

A job that cannot start until another job has finished. The noticeboard hangs on the flat, so the flat must be standing first.

Parallel

Jobs happening at the same time on different crew. 4 crew working at once finish far sooner than 1 person doing every job in turn.

IF and REPEAT

IF gives an instruction for each of 2 outcomes (the table clears the door, or it does not). REPEAT writes an instruction once and runs it for every chair.

DCF: Data and computational thinking → Problem-solving and modelling Strike means take off stage · set means put on stage

Slide 3 of 7 · Steps 1 and 2: 2-person jobs and dependencies · Drama · Year 8

11 minutes

Step 1 & Step 2: circle the 2-person jobs, then write what each setting job waits for

Step 1 (4 min): read the brief and both lists. Circle every job that needs 2 people. Step 2 (7 min): next to each job on the setting list, write what must be struck or set first. Copy the first dependency from the board.

Setting job	What must happen first
Vending-machine flat (2 people, 20 s)	It stands where the kitchen table was, so the table must be struck before the flat comes on.

Steps 1 and 2 on your worksheet · 11 minutes, on your own Most jobs depend on nothing: say so, that is useful

Supply teacher script (no subject knowledge needed)

Say aloud: “Four minutes: read both lists and circle every job that needs 2 people. Then 7 minutes: for each job on the setting list, write next to it what has to be struck or set before it can start. The first one is on the board. If a job depends on nothing, write none.”

Quick check: the 2-person jobs are the kitchen table (12 s) and the vending-machine flat (20 s). Dependencies: the flat waits for the table to be struck; the noticeboard waits for the flat to be standing; the chair stacks go where the kitchen chairs were, so all 4 kitchen chairs must be off first, which takes 16 s. Nothing else depends on anything: rug, props, water cooler, magazines and sign can all run at the same time as everything else.

Slide 4 of 7 · Step 3: the timing table · Drama · Year 8

14 minutes

Step 3: fill the timing table, one column per crew member

Write start and finish seconds for every job in the columns for Crew A, B, C and D. Obey the door rule (no more than 2 in the upstage doorway) and the dependencies from Step 2. Copy the first row from the board, then plan the rest. Finish with the total time and the seconds to spare out of 90.

Seconds	Crew A	Crew B	Crew C	Crew D
0 to 8	Table off, with B (upstage door)	Table off, with A	Kitchen chairs off, stage right	Kitchen props into the box

Step 3 on your worksheet · 14 minutes, in pencil Waiting is allowed if you can say what it is waiting for

Supply teacher script (no subject knowledge needed)

Say aloud: “The first row is on the board: A and B start the table together, C starts the 4 kitchen chairs, D clears the props. Copy it, then plan every job down the table in pencil. A crew member may wait, but you must know what they are waiting for. At the bottom, write your total time and the seconds to spare out of 90.”

Quick check: the worked example finishes in 55 seconds with 35 to spare. The jobs add up to 116 seconds of work (44 s striking, 72 s setting); 4 crew in parallel do it in 55 because the change is limited by its longest chain, table then flat then noticeboard. In the example: table off ends at 12; flat on 12 to 32; noticeboard 32 to 40; C does chairs to 16, rug 16 to 24, chair stack 1 on 24 to 34, then aligns 3 chairs; D waits from 8 to 16 for the kitchen chairs to be clear, then stack 2 on 16 to 24, aligns to 32, magazines and sign to 38; B sets the water cooler 32 to 38; all 4 check the stage 40 to 55. Any total under 90 with no rule broken and no dependency broken is acceptable; a pupil whose total is 116 has not used the crew in parallel.

Slide 5 of 7 · Steps 4, 5 and 6: IF, REPEAT, dry run, one fix · Drama · Year 8

13 minutes

Step 4, Step 5 & Step 6: write your IF and REPEAT, then let a partner break it

Step 4 (5 min): write your IF statement for the table legs and your REPEAT statement for the chairs in the 2 boxes. Step 5 (6 min): swap with a partner. Read their algorithm aloud one step at a time and fill their dry-run table: Works? If it breaks, what breaks. Step 6 (2 min): take your sheet back and write the one change you would make.

IF model: IF the table clears the upstage doorway THEN carry it straight off (12 s) ELSE fold the legs first (+10 s), then carry it off.

REPEAT model: REPEAT FOR EACH of the 3 chairs in stack 1: line it up with its tape mark (2 s each).

Steps 4 to 6 on your worksheet · 13 minutes, pairs for the dry run Your partner fills your dry-run table in their handwriting

Supply teacher script (no subject knowledge needed)

Say aloud: “Five minutes: write your IF for the table legs and your REPEAT for the chairs. Both branches of the IF need an instruction; do not just hope. Then swap sheets. Read your partner’s algorithm out loud one step at a time and tick or break each step in their dry-run table. Try to break it. Last 2 minutes: sheets back, write the one change you would make.”

Quick check, the IF: if the legs have to be folded, everything on the A and B track shifts by 10 s: the flat is up at 42, the noticeboard at 50, the check runs 50 to 65. Worst case 65 seconds, 25 to spare. A secure IF carries that 10 s through the rest of the plan rather than stopping at the table.

Walk the room, the dry run: the worked example dry run broke 1 step: “D: chair stack 2 on at 8” failed because 2 kitchen chairs were still in that row at 8 s; the fix was D waits until 16. The example’s one change: move the noticeboard from A to D, because D is finished at 38 and A is the one who might be 10 seconds late, which drops the worst case from 65 s to 57 s. Any fix is acceptable if it is argued from the timings.

Slide 6 of 7 · Self and partner check · Drama · Year 8

3 minutes

Check your algorithm against the success criteria

Tick each criterion your work meets. Your partner then checks your IF: does it give an instruction for both outcomes?

I broke the change down into jobs and worked out which ones depend on another job finishing first.
I used the 4 crew in parallel, so my total time is much less than the 116 seconds of work.
I handle the table-leg problem with an IF, giving an instruction for both outcomes.
I used a REPEAT for the chairs rather than writing the same instruction out 6 times.
I tested my algorithm by having somebody else follow it exactly, and I recorded what they found.

3 minutes · partner check Finished early? Redo it with 3 crew: what is the new bottleneck?

Supply teacher script (no subject knowledge needed)

Say aloud: “Tick the 5 criteria. Then your partner reads your IF: if it only says what happens when the table clears the door, write ELSE beside it and fix it.”

Extension answers: with 3 crew the table and the flat still need 2 people each, so the third crew member carries everything else alone and the chairs and rug become the bottleneck; the change is longer than 55 s but should still beat 90. The second IF about the brace belongs just after the flat is stood up, before the noticeboard, and the free crew member (D in the example) fetches the brace. The reverse change: chairs, rug and props are the same steps backwards; the flat and noticeboard are not, because the noticeboard must come off before the flat and the flat before the table goes on.

Slide 7 of 7 · Plenary review · Drama · Year 8

3 minutes

Round the room, then quick-check answers before handing in

Everyone says their total time in seconds and names 1 job they ran in parallel. Then check these answers.

Question	Correct answer
How many seconds of work are there in total, and how fast can 4 crew do it?	116 seconds of work, done in 55 seconds in the worked example, 35 to spare out of 90.
What is the longest chain that limits the change?	Table, then flat, then noticeboard. Each must finish before the next can start.
What is the worst case if the table legs have to be folded?	65 seconds: every A and B job shifts by 10 s. Still 25 seconds to spare.

Check your name and class are on your worksheet Worksheets in · the dry-run table must be in your partner’s handwriting