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 14 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.

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.
2.Read the text, then answer the questions.

The Wolves and the Rivers

Wolves were shot out of Yellowstone by 1926. Fourteen were brought back in 1995. With no wolves, elk had grazed the valleys freely for seventy years. Young willow and aspen were eaten as soon as they grew. The wolves killed some elk. More importantly, they changed where elk would stand still. Open valley floors became dangerous, so the elk stopped lingering there. Willow and aspen grew back along the rivers. Beavers, which need willow, returned. Their dams made ponds. Roots held the banks. The rivers narrowed, deepened and moved less. Some researchers describe this as wolves changing the shape of rivers, though others argue the effect has been overstated.

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

LessonPrint · RI.4.2 · Set 14 · free to copy for classroom use

Answer key — Main Idea and Its Support

Set 14. Prints on its own sheet.

  1. 1.1. Discovering penicillin was only the start — the details about Florey, Chain and two thousand litres show that making it usable was the real work.
  2. 2.1. Returning wolves changed the whole valley through a chain of effects — supported by the elk behaviour, the trees, the beavers and the rivers.

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.