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Computer Science and Digital Literacy · 35 minutes

Suggested grades 9–12 · Unit 2: Data quality and representation · Lesson 1 of 2

Data Cleaning with a Decision Log

Preserve missingness and document transformations in a fictional data table.

Mr. S Teaches · Original starter lesson · HS-CS-03 · Grade range is planning guidance.

Watch, notice, discuss

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OPTION 1 · YOUTUBE

Code.org Lesson 3 Filtering and Cleaning Data Tutorial | Unit 9 Data C.S. Principles + CodeAI

By Mr. Kaiser

Use a data-cleaning and filtering walkthrough as a tool-based comparison; the lesson’s decision log is done on its own supplied data.

Open on YouTube: Code.org Lesson 3 Filtering and Cleaning Data Tutorial | Unit 9 Data C.S. Principles + CodeAI (opens a new tab) ↗
After watching

Which cleaning decision could change the result, and how would another analyst reproduce it?

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Learning objective

Apply stated cleaning rules and write a reproducible technical report distinguishing missing from zero.

Before you begin

  • Tables
  • Mean calculation

Gather your materials

  • Paper and pencil
  • The fictional table supplied here
  • Optional offline spreadsheet

Language to know

missing value
A measurement not recorded or unavailable, distinct from a measured zero.
validation rule
A stated test for whether a value fits the intended format or range.
provenance
The record of where data came from and how it changed.

Understand the concept

Fictional weekly reading table: A:20 minutes; B: blank; C:0 minutes; D:“15 min”; E:−4 minutes. A documented rule accepts nonnegative numerical minutes, parses an explicit“min”suffix and flags negatives for review; blanks stay missing. Converting all problematic entries to 0 would invent observations and bias a mean. Keep the original table and a change log so another person can reproduce the work.

Teach it step by step

  1. Copy the original table without overwriting its entries.
  2. Apply the rules to each row, labeling accepted,parsed,missing or flagged.
  3. Calculate a mean only for the three valid recorded values 20,0,15 and state the denominator.
  4. Write a short method report with the rules,change log,result and unresolved rows; ask a partner to reproduce it.

Make the thinking visible

Worked example or model response

Accepted values are 20,0 and 15, sum 35 over 3 recorded observations, mean 35/3≈11.67 minutes. B remains missing and E is flagged, not silently corrected. Treating both as 0 would instead give 7 minutes and imply two unsupported measurements.

Guided practice

Apply the same rules to 7,“8 min”,blank,−2 and 0. Write the cleaned values and status labels.

Independent practice

1. Find the valid-record mean for the guided data. 2. Write a two-sentence report explaining why blank and 0 require different labels. 3. Identify what must be asked before correcting−2.

Quick assessment

Why should the original values remain available after cleaning?

Answer key & assessment criteria

Answers and teaching guidance

  1. Guided: Valid 7,8,0; one missing and one flagged.
  2. Independent 1:15/3=5 minutes. 2: Zero records a measured absence of minutes; blank records no measurement, so it should not enter the same denominator. 3: Check the source or collection process rather than guessing the intended value.
  3. Quick check: They preserve provenance,allow review of decisions and help correct an erroneous transformation.

Look for: Require the learner to explain the interpretation and check, not only state a result. Assess the written trace or evidence record; do not request real passwords, accounts or personal data.

Make it work for your learner

More support

Provide separate original,value,status andreason columns; use a calculator after classification.

Extension challenge

Compare two justified handling policies and explain how each changes what the resulting statistic means.

Verified references · Selected contributions

Standards connections

Subject-content alignment not yet verified

Supporting literacy connections

These records apply to the specified reading, writing or communication task. They do not establish subject-content alignment.

Supporting Common Core connection

WHST.9-10.2

Common Core · Grades 9–10

Write an explanatory technical method and result report with definitions and concrete examples.

Read the official standard ↗

Supporting grades 9–10 technical-literacy practice in the stated task, not a verified computer-science content alignment or full text-complexity assessment.

Verified 2026-11-04. Selected contribution, not full attainment.