Main Idea Detectives Worksheet
Reading Comprehension Lab
Main Idea Detectives
Detective:
Date:
Detective Field Rule: The Main Idea is the big umbrella—the central point the author wants you to remember. The Supporting Details are the clues, facts, and reasons that hold that umbrella up!
Case File 01 | Nature's Living Flashlights
Lexile: 720L
On warm summer evenings, meadows sparkle with tiny blinking lights. These belong to fireflies, but these fascinating insects do not glow just to put on a show. Fireflies use their glowing lights to survive and communicate. Each species of firefly flashes its own special pattern of light, like a secret code, to help them find a mate in the dark. Furthermore, the chemical reaction that produces their light tastes extremely bitter to predators. When a hungry bat or frog spots the bright flash, it quickly remembers the foul taste and flies away. Some firefly larvae even flash their lights underground to warn predators to keep their distance.
1
Crack the Case: Evidence Organizer
Central Main Idea: What is this entire passage mostly about? Write in 1 complete sentence
Clue / Detail 1
Clue / Detail 2
Clue / Detail 3
2
Detective Evaluation: Best Summary
Which statement best states the main idea of Case File 01?
A Fireflies flash their lights primarily to look beautiful in grassy summer fields.
B Fireflies produce glowing light as an essential tool for survival and communication.
C Predators such as bats and frogs love the sweet flavor of glowing fireflies.
D All flying insects use special chemical reactions to glow brightly in the dark.
Unit 4: Informational Text Analysis Page 1 of 2
Independent Case Investigation
Case File 02: Rainforests of the Sea
Level 4 Analysis
Reading Passage
Lexile: 740L
Although coral reefs cover less than one percent of the ocean floor, they are vital ecosystems that support a huge variety of marine life. Often called the "rainforests of the sea," coral reefs provide shelter and nursery grounds for more than 25 percent of all ocean species, including clownfish, sea turtles, and eels. In addition to housing marine animals, reefs act as giant underwater barriers that protect coastlines from powerful storm waves and erosion. Furthermore, millions of people around the globe rely on healthy coral reefs for their daily food and livelihoods through fishing and tourism. Protecting coral reefs is essential for both ocean animals and human communities.
3
State the Central Idea
In your own words, write a complete sentence stating what the author wants readers to know about coral reefs.
4
Evidence Locker: Two Strongest Supporting Details
Find and write two distinct facts from the passage that support the central main idea you identified above.
Fact Clue A:
Fact Clue B:
5
Spot the Imposter: Off-Topic Detail
A careful detective spots clues that don't belong! Which sentence does NOT support the author's main idea about coral reefs?
A Reefs provide vital shelter for more than one-fourth of all marine animals.
B Coral reefs protect fragile coastlines by absorbing dangerous storm waves.
C Scuba diving gear was invented by Jacques Cousteau in the twentieth century.
D Coastal communities depend on healthy reef fish for food and their local economy.
Detective Mastery Score: / 5 pts Page 2 of 2
Main Idea Detectives Answer Key
Teacher Answer Key & Scoring Guide
Main Idea Detectives
Official Key
CCSS.ELA-LITERACY.RI.4.2
Scoring Scale: 5 total question sets (7 assessment points)
Page 1: 3 pts • Page 2: 4 pts • Mastery: 6/7 pts (85%+)
1 Question 1: Evidence Organizer Solutions
2 Points Total
Exemplar Central Main Idea (1 pt): Full Credit Criteria
"Fireflies produce glowing light as an essential tool to survive, communicate with mates, and ward off predators."
Look-Fors: Student must state why they glow (survival, finding mates, or deterring predators), not just that they glow. Topic alone ("Fireflies") receives partial credit (0.5 pt).
Exemplar Supporting Details (1 pt total - any 2-3 of these):
Clue A: Mating
Each species flashes its own secret pattern/code to attract and find a mate in the dark.
Clue B: Bad Taste
Their chemical reaction tastes bitter; predators like bats and frogs remember the bad taste and leave.
Clue C: Larvae Defense
Firefly larvae flash underground to warn predators to stay away.
2 Question 2: Multiple Choice Evaluation
1 Point
B
CORRECT: "Fireflies produce glowing light as an essential tool for survival and communication."
Captures both key aspects of the passage: the biological function (survival/defense) and social function (communication/mating).
Distractor Analysis:
Choice A: Incorrect. The passage explicitly states they do not glow just to put on a show or look pretty.
Choice C: Incorrect. The text states fireflies taste bitter and foul to predators, not sweet.
Choice D: Incorrect. Overgeneralization ("all flying insects"). The passage is specifically about fireflies.
Teacher Resource • Case File 01 Key Page 1 of 2
Independent Investigation Key
Case File 02: Rainforests of the Sea
4 Points Total
3 Question 3: Central Idea Statement (1 pt)
Constructed Response
Exemplar Student Statement:
"Coral reefs are vital ecosystems that protect coastlines, support thousands of sea animals, and provide food and jobs for humans."
Scoring Guidance: Accept any complete sentence that connects the ecological value of reefs (supporting sea life) to their importance for coastlines/humans.
4 Question 4: Evidence Locker (2 pts - 1 pt per fact)
