How to run a Do Now in Computer Science

By Ash, Computing teacher and founder of RADevo · 9 October 2026 · 6 minute read

A Do Now is a short task waiting on the board when students walk in. Done well, it settles the class, gets every student thinking within seconds and brings back content they'd otherwise forget. Here's how to plan one for Computer Science, with example questions you can use tomorrow.

Why bother with a Do Now?

• Calm, purposeful starts. Students know there's always something to do, so the first few minutes aren't lost.
• Daily review. Rosenshine's Principles of Instruction (2012) start with "begin a lesson with a short review of previous learning". A Do Now is that review.
• Spaced retrieval. Bringing back older topics, not just last lesson's, is what makes knowledge stick. See Retrieval practice in Computing.
• Quick assessment. A glance round the room tells you what the class has and hasn't remembered before you build on it.

A simple structure: four questions, five minutes

Keep each question answerable in about a minute. The Do Now is a warm-up, not a mini-exam.

Example Do Now: GCSE Computer Science

Suppose today's lesson is on searching algorithms (OCR J277 2.1):

1. What must be true about a list before you can use a binary search on it?
2. Give one reason why a solid state drive might be chosen over a magnetic hard disk drive for a laptop.
3. State the purpose of the program counter (PC) in the CPU.
4. Convert the denary number 45 into 8-bit binary.

Answers: the list must be sorted; for example it's more durable (no moving parts), faster or quieter; it holds the address of the next instruction to be fetched; 00101101.

Notice that only the first question links to the current topic. The other three come from topics taught weeks or months ago, which is where the spacing benefit comes from.

Example Do Now: A Level Computer Science

At A Level the same structure works, but the questions can ask for a little more reasoning. Suppose last lesson introduced stacks and queues (OCR H446 1.4.2) and today moves on to linked lists:

1. A stack is empty. The values 4, 7 and 9 are pushed in that order, then one value is popped. Which value is popped?
2. State one difference between a compiler and an interpreter.
3. Give the time complexity of a binary search in Big O notation.
4. Explain why a normalised floating point number gives the greatest precision for a given number of bits.

Answers: 9 (last in, first out); for example a compiler translates the whole program into object code before it runs, while an interpreter translates and runs it one line at a time; O(log n); there are no wasted leading bits in the mantissa, so every bit adds precision.

For the last question, accept any answer that captures the idea and use the review time to sharpen the wording. A Level students benefit from hearing what a full-mark answer sounds like, so read one out or show a model answer on the board.

Example Do Now: KS3 Computing

With younger students, keep the questions short and the wording simple. Multiple choice and true or false questions work well because they're quick to mark. Suppose last lesson was on spreadsheets:

1. In a spreadsheet, what does a cell reference such as B3 tell you?
2. True or false: a strong password should include your name so you can remember it.
3. What does the CPU do? (a) stores files, (b) processes instructions, (c) shows the picture on screen
4. What is the binary number 101 in denary?

Answers: the column (B) and row (3) of the cell; false; (b); 5.

Good Do Now questions are…

• Short and specific. "State the purpose of…" beats "Explain everything you know about…".
• Answerable alone. No textbook, no help: that's what makes it retrieval.
• A mix of recall types. A definition, a calculation, a one-line explanation, a trace of three lines of code.
• Chosen from real gaps. The most useful question is often the one most of the class got wrong in homework.

Running it

1. Have it on the board before they arrive. Students start straight away, in silence, on paper or mini whiteboards.
2. Time it. A visible timer of four or five minutes keeps the pace up.
3. Go through answers quickly. Reveal them, have students self-mark in a different colour pen and correct anything wrong.
4. Check the room. "Hands up if you got question 3" tells you whether to re-teach it now or come back to it next week.

Common pitfalls

• Only asking about last lesson. That's useful, but it misses the spacing benefit. Always include something older.
• Letting it drift to 15 minutes. Keep feedback brisk; long discussions belong in the main lesson.
• Making it high stakes. Don't record scores or rank students. Wrong answers should feel safe.
• Spending ages writing it. A Do Now should take minutes to plan. Keep a bank of questions by topic and reuse them.

How RADevo helps

RADevo's Do Now builder picks the four questions your class got wrong most in the last week (one per topic where it can), and you can swap, pin or add any question. Press Present and it goes on the board with a timer, and R reveals the answers. The same screen has slides for homework set, a hall of fame and the class's learning journey. If you want ready-made questions to start with, our free revision quizzes cover the GCSE, A Level, Cambridge Nationals, BTEC and KS3 courses listed on that page.

References

• Rosenshine, B. (2012). Principles of Instruction: research-based strategies that all teachers should know. American Educator, 36(1), 12–19, 39.