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This Subtraction Within 20 drill has 40 problems for Grade 1. Windmills theme. Answer key included.
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Max's windmill is spinning wildly out of control! He must solve subtraction problems to stop the giant blades before they crash.
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 develop number sense and flexible thinking about quantities. At six and seven years old, children are building the mental math foundation they'll rely on for decades—this is when their brains are most ready to see numbers as relationships rather than just symbols. Mastering subtraction-within-20 lets students solve real problems: sharing snacks, figuring out how many toys are left after giving some away, or determining which group has fewer items. This skill also builds confidence, because once children can reliably subtract within 20, larger numbers feel less intimidating. Beyond math class, subtraction-within-20 strengthens working memory and logical reasoning—skills that support reading comprehension and problem-solving across all subjects. Students who are comfortable with these facts are also better equipped to handle word problems and to notice patterns in math.
What your student will practice
- Fluently subtract single-digit numbers from numbers within 20 using strategies
- Count back or use ten-frames to solve subtraction problems accurately
- Recognize and apply the inverse relationship between addition and subtraction
- Model subtraction-within-20 using objects, drawings, or mental math
Common mistakes to watch for
Many first graders confuse the direction of subtraction and start counting up instead of back, or they lose track while counting and recount the starting number by mistake. You'll spot this when a child subtracts 15 – 3 and counts "15, 14, 13, 12" but then says 15 instead of 12—they've included the starting number in their count. Another common error is 'fence-post counting,' where students count the spaces between numbers rather than the numbers themselves when using a number line. Watch for answers that are consistently one too many or one too few; that's usually a counting error, not a conceptual misunderstanding.
Use a simple "take away" game with small objects like crackers, blocks, or coins at home. Say a subtraction sentence aloud ("We have 14 crackers. Let's eat 5. How many are left?"), have your child move the items into two piles, count what remains, and say the answer. This turns subtraction into a tactile, speaking activity rather than just pencil-and-paper work. Rotate who creates the problem—when children invent their own subtraction scenarios, they internalize the concept much faster than drilling facts alone.