Skip to content
LessonPrint

Main Idea and Its Support is a free printable Grade 4 English worksheet on stating a main idea and how the details hold it up, aligned to Common Core standard RI.4.2. It prints 2 questions with an answer key on its own sheet of paper, in 25 versions, 21 of them with different questions, so no two pupils in the class work from the same page. Print it from the browser or download it as a PDF — no account, no email.

Set 2 of 25 · the same problems every time you open this link.

Next setLesson plan

One paper per pupil

12345678910111213141516171819202122232425

Set 1 has all 25 in a single PDF. 21 of these 25 sets ask different questions — this skill does not have 25 questions to give. The rest reorder them, so no two pupils have the same paper in front of them.

Main Idea and Its Support

RI.4.2

NameDate

Read the text, then answer the questions.

1.Read the text, then answer the questions.

Lichen

A lichen is not one organism. It is a fungus and an alga living as one body. The fungus provides the structure and holds water. The alga photosynthesises and makes sugar. Separated, the fungus starves and the alga dries out. Because it needs no soil, a lichen can grow on bare rock, on gravestones and on the roofs of cars that have not moved for a decade. Lichens grow extremely slowly — some crustose species less than a millimetre a year. Scientists use that rate to date rock surfaces, a method called lichenometry. Lichens also absorb whatever is in the air. Where the air is dirty, they disappear, which makes them a living measure of pollution.

  1. 1. Determine the main idea of this text and explain how key details support it.
2.Read the text, then answer the questions.

How Penicillin Was Found

In 1928 Alexander Fleming went on holiday and left a stack of dishes on a bench. Each held a colony of bacteria. When he came back, one dish had a spot of mould on it. Around the mould was a clear ring where the bacteria had died. Fleming realised the mould was producing something that killed bacteria. He named it penicillin and published a paper. Almost nobody noticed. Ten years later, Howard Florey and Ernst Chain read that paper and tried to make penicillin in quantity. That turned out to be the hard part: it took two thousand litres of mould fluid to treat one patient. By 1944 the problem had been solved and penicillin was reaching soldiers in the field.

  1. 1. Determine the main idea of this text and explain how key details support it.

LessonPrint · RI.4.2 · Set 2 · free to copy for classroom use

Answer key — Main Idea and Its Support

Set 2. Prints on its own sheet.

  1. 1.1. A lichen is a partnership that can live where nothing else can — supported by the bare rock, the slow growth and the pollution sensitivity.
  2. 2.1. Discovering penicillin was only the start — the details about Florey, Chain and two thousand litres show that making it usable was the real work.

More practice for RI.4.2

State the main idea, show the details behind it, and summarise.

Teaching this next? The Main Idea and a Summary is the 40-minute plan for it, with the misconceptions to expect.

All Grade 4 worksheets

Last reviewed 2026-09-05. Aligned to RI.4.2 of the Common Core State Standards for English language arts.