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This Subtraction Within 20 drill has 40 problems for Grade 1. Groundhog Day theme. Answer key included.
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Max discovered 17 acorns scattered in Groundhog's burrow. He must collect them before hibernation time!
Standard: CCSS.MATH.1.OA.C.6
Preview
Page 1 — Drill
Page 2 — Answer Key
What's Included
About this Grade 1 Subtraction Within 20 Drill
Subtraction within 20 is a cornerstone skill that helps first graders move beyond counting on their fingers and develop true number sense. At ages 6-7, children are building mental math fluency—the ability to quickly and accurately solve problems they'll encounter daily, from sharing snacks with classmates to figuring out how many crayons are left in a box. When students master subtraction within 20, they're not just memorizing facts; they're learning that numbers can be decomposed and reorganized, a foundational concept for algebra later on. This skill also builds confidence and independence, allowing children to solve simple word problems without adult support. Regular practice with subtraction within 20 strengthens working memory and helps students recognize patterns (like how 15 - 5 and 14 - 4 both equal 10), which accelerates their overall math development. By the end of first grade, fluency with these problems directly supports reading comprehension of math word problems and prepares them for addition and subtraction within 100 in second grade.
What your student will practice
- Solve subtraction problems with minuends up to 20 accurately and fluently
- Use strategies like counting back, part-whole thinking, and ten-frames
- Recognize and apply the inverse relationship between addition and subtraction
- Explain subtraction using manipulatives, drawings, or words
Common mistakes to watch for
Many first graders confuse the order of numbers in subtraction, starting with the smaller number instead of the larger one—for example, solving 15 - 8 by saying "8 take away 15" instead. Another frequent error is miscounting when they use the counting-back strategy; they often forget to count the starting number or recount it, landing on the wrong answer. Some students also struggle with teen numbers (13-19) specifically because they haven't yet internalized that these are "ten and some ones," so 16 - 3 feels as unfamiliar as 26 - 3. Watch for hesitation on problems with the same minuend but different subtrahends (like 12 - 2, 12 - 5, 12 - 7), which signals they haven't yet chunked the number 12 as a unit.
Use a simple game like 'Subtract and Win' with two dice and a pile of 20 small objects (buttons, crackers, or blocks). Roll both dice, add them together, then remove that many objects from the pile. Ask your child, 'How many are left?' Repeat until the pile is gone. This mimics the groundhog peeking out and counting seeds in a burrow—it's concrete, engaging for a 6-year-old, and lets them practice subtraction within 20 without the pressure of a formal problem. Playing this twice a week for five minutes builds automaticity faster than worksheets alone.