Download clean, printable lists of the most common mistakes students make — so you can fix them before they cost marks.
Each sheet is aligned to its exam board and built from recurring student errors highlighted in examiner reports and mark schemes.
What you get
A topic-by-topic mistakes list with a “do this instead” fix and a quick self-check.
How to use it
Review before past papers, then use the quick checks to catch errors under timed conditions.
Why it works
Many marks are lost on predictable slips: rounding, sign errors, units, and misreading commands.
Coverage by topic
Preview (up to 5 per topic)
38 total rows in download
| Topic | Common mistake / misconception | Do this instead | Quick check |
|---|---|---|---|
| Algorithms | Confusing iteration with selection. | Loop repeats; if/else chooses paths. | Is a condition repeatedly tested? |
| Algorithms | Infinite loop risk ignored in trace tables. | Check update step inside loop variables; verify exit condition can become true. | Does the loop variable change each pass? |
| Logic | AND/OR truth table errors near exam pressure. | AND needs both true; OR needs at least one true; write tiny truth table if unsure. | Test one row you know (T,T). |
| Binary arithmetic | Binary addition without carrying. | Track carry bit column by column like base-10. | Did you write carries above? |
| Hex & colour | Hex digit treated as one bit. | Each hex digit = 4 bits; two hex digits = 1 byte. | 8-bit colour → how many bits per channel if question defines it? |
| Compression | Lossy described as ‘smaller and identical’. | Lossy removes irreversible detail; lossless fully recoverable. | Can you reconstruct exact original? |
| Networks | IP address confused with URL or domain. | URL locates resource; domain is human-readable; IP is numerical address. | Which layer of naming are you using? |
| Networks | Packet switching described as ‘whole file sent at once’. | Data split into packets routed independently with sequence info. | Did you mention packets can take different routes? |
| Protocols | HTTP described as transport protocol. | HTTP is application layer; TCP is transport (connection-oriented) often paired. | Which OSI layer does your textbook use? |
| Security | Encryption described as authentication. | Encryption protects confidentiality; authentication verifies identity. | Is the problem about eavesdropping or impostors? |
| Security | Firewall described as antivirus. | Firewall filters traffic by rules; antivirus detects malware patterns. | Network vs device protection? |
| Programming | Off-by-one errors in list indexing (0 vs 1). | State language rules; loop from 0 to length-1 for full traversal. | What is the last valid index? |
| Programming | = used for comparison instead of == in pseudocode/exam dialect. | Follow the exam reference language: match symbols exactly as taught. | Did you reread pseudocode rules? |
| Programming | Scope confusion: variables inside function not accessible outside. | Track local vs global; minimise globals. | Where was it declared? |
| Programming | String vs integer concatenation producing nonsense when adding. | Cast/parse consistently before arithmetic. | Is input text or number? |
| SQL | SELECT * when you only need columns for joins. | Name columns; ensure JOIN condition includes primary/foreign key match. | Did you write ON ...= |
| SQL | DELETE without WHERE in exam-style tasks (dangerous conceptually). | Always constrain deletions in exam answers unless truncating whole table intentionally. | Would you wipe all rows in real life? |
| Boolean algebra | De Morgan errors when negating AND/OR. | NOT(A AND B) = (NOT A) OR (NOT B); practise with tiny examples. | Did you flip AND↔OR? |
| Hardware | RAM described as permanent storage. | RAM is volatile; secondary storage is non-volatile for persistence. | Loses data on power off? |
| CPU | Clock speed said to be the only determinant of performance. | Mention cores, cache, architecture, RAM, storage type as appropriate. | Did you give at least two factors? |
| Translators | Interpreter and compiler differences reversed. | Compiler: whole program to machine code before run; interpreter line-by-line. | Are errors found before or during run? |
| Ethics | GDPR reduced to ‘companies must delete data’ only. | Mention lawful basis, consent, access rights, data minimisation as taught. | Did you name more than deletion? |
| Environmental | E-waste described vaguely without disposal/recycling angle. | Landfill toxins, recycling recovery of metals, refurbishment. | Did you name one hazard and one solution? |
| Data integrity | Validation described as verification. | Validation checks plausibility; verification checks accuracy when entered. | Is data reasonable vs is it copied correctly? |
| Programming logic | Nested if-else matched to wrong condition due to indentation only in mind. | Trace with a table for two inputs; bracket conditions clearly. | Did you test a boundary case? |
| Exam technique | Trace table missing column for every variable that changes. | Add columns for all updated variables; show output rows. | Does every line update something? |
| Exam technique | Writing JavaScript syntax when answer expects structured English/pseudocode. | Match the paper's language: AQA often wants neutral language steps. | Copy style from specimen answers. |
| Exam technique | Long prose for a 2-mark ‘give two’ algorithm improvement. | Two short bullet improvements (input validation, exception handling, etc.). | Exactly two distinct points? |
| Exam technique | No test plan for a program question asking for test data. | Normal, boundary, invalid — three cases typical. | Did you include one invalid? |
| Exam technique | Forgetting to label outputs in algorithm trace. | Show OUTPUT line explicitly when PRINT occurs. | Would a marker see the printed value? |
| HTML/CSS context | Accessibility ignored for web questions (alt text). | Mention alt text, contrast, semantic tags if asked to improve usability. | Did you name one accessibility fix? |
| Searching | Binary search said to work on unsorted lists. | Requires sorted data; compare midpoints iteratively. | Was the list sorted first? |
| Sorting | Claiming O(n) for comparison sorts when taught simply. | Match bubble vs merge expectations to your teaching depth; avoid overclaiming. | Stick to spec wording. |
| Floating point | Rounding errors ignored in equality checks conceptually. | Compare within epsilon if teaching mentions limits of binary fractions. | Are you comparing == on floats in logic questions? |
| Logic circuits | NOT gate drawn wrong on truth table. | Copy symbols carefully; invert output column. | Does 0→1 and 1→0? |
| Cyber | Phishing vs pharming confused. | Phishing tricks users; pharming redirects traffic/DNS threat (as taught). | Is deception social vs technical? |
| Databases | Primary key described as ‘any field’. | Unique identifier; cannot be null; each row one value. | Could two rows share the PK? |
| Databases | Redundancy confused with backup. | Redundant data duplicated across table; normalisation reduces it. | Same fact stored twice? |
A checklist blending theory slips (binary/logic, networks, ethics) with typical exam mistakes on trace tables, pseudocode and skeleton programs.
If your centre runs the NEA, follow your teacher and the latest AQA NEA authentication guidance. This list does not replace official rules on collaboration and internet use.