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What Happened and Why is a free printable Grade 4 English worksheet on explaining an event using the text's own information, aligned to Common Core standard RI.4.3. It prints 2 questions with an answer key on its own sheet of paper, in 25 versions, 19 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 21 of 25 · the same problems every time you open this link.

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Set 1 has all 25 in a single PDF. 19 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.

What Happened and Why

RI.4.3

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. Explain the relationship between Fleming's paper and Florey and Chain's work.
2.Read the text, then answer the questions.

What a Beaver Dam Does

A beaver does not build a dam for shelter. It builds one to make a pond, and it lives in a lodge in the pond. The dam raises the water so the lodge entrance stays underwater. A predator that cannot swim cannot get in. But the pond does far more than protect one family. Behind a dam, water slows, and slow water drops the silt it carries. Over years this builds rich wet ground. That ground holds water in a drought and holds it back in a flood. It supports plants, insects, amphibians and birds that were not there before. Where beavers have been reintroduced, the number of species in a valley typically rises within five years.

  1. 1. Explain the relationship between the dam and drought protection.

LessonPrint · RI.4.3 · Set 21 · free to copy for classroom use

Answer key — What Happened and Why

Set 21. Prints on its own sheet.

  1. 1.1. They read the paper ten years later and took on the problem Fleming had not solved: producing penicillin in quantity.
  2. 2.1. The dam slows water, silt builds rich wet ground, and that ground holds water through a drought.

More practice for RI.4.3

Explain what happened and why, using the text's own information.

Teaching this next? Explaining Events, Procedures and Ideas is the 40-minute plan for it, with the misconceptions to expect.

All Grade 4 worksheets

Last reviewed 2026-09-05. Aligned to RI.4.3 of the Common Core State Standards for English language arts.