Before you start
Most popular
Number Studio Build a number from thousands to ones — watch standard, expanded & word forms update, and regroup 10-for-1. 
Number Line Place a number, round, work with integers & absolute value — solve by choosing your own jumps. 
Integer Order Which is larger — -3 or -5? Predict, then watch both land on the line. 
Rekenrek A quick-look bead rack — see a quantity in fives and tens, and build make-ten pairs. All activities
Build & reason
Number Studio Compose a number from base-ten blocks; standard/expanded/word forms update as you trade 10-for-1. Number Line Place, round to the nearest ten or hundred, and work with integers and absolute value. Integer Order Predict which negative is larger, then watch both land — beats the “bigger digit” trap. Rekenrek See quantities in fives and tens without counting; build make-ten pairs.
Practice & play
Practice the concepts 12 kits from place value up to integers & absolute value, with a hint whenever you get stuck. Number Duel Head-to-head kit round for 2–4 players — one device or an online room by code. No chat, no accounts. Mixed Practice Shuffles the kits you’ve learned and brings them back when they’re ready to review. Teach the Cast Teach a number-sense idea to a cast member still learning it — teaching makes it stick.
Concept Kits — 12 kits of number sense
Kit 1: Place Value: Whole Numbers Place value · grades 4-5 · 25 questions Kit 2: Place Value: Decimals Place value · grades 6-7 · 25 questions Kit 3: Multi-Digit Addition & Subtraction Operations · grades 4-5 · 25 questions Kit 4: Multi-Digit Multiplication Operations · grades 4-5 · 25 questions Kit 5: Division with Remainders Operations · grades 4-5 · 25 questions Kit 6: Estimation Strategies Estimation · grades 6-7 · 25 questions Kit 7: Properties of Operations Operations · grades 6-7 · 25 questions Kit 8: Factors & Multiples Factors & primes · grades 4-5 · 25 questions Kit 9: Prime & Composite Numbers Factors & primes · grades 4-5 · 25 questions Kit 10: Integers on a Number Line Integers · grades 6-7 · 25 questions Kit 11: Integer Operations Integers · grades 8-9 · 25 questions Kit 12: Absolute Value & Order Integers · grades 6-7 · 25 questions
For grown-ups — progress report →
Think it through first
More ways to play
😄 Brain break
Meet the cast — the characters who teach this
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Tenfold Place value — powers of 10, positional notation -
Zeph The zero placeholder — its load-bearing role in positional notation -
Mirror Negative numbers — reflection across zero on the number line -
Skip Skip-counting and multiples — repeated addition as forward stepping -
Tug Inverse operations — addition ↔ subtraction (and the same idea for × ↔ ÷) as opposite pulls on the same line -
Nigh Rounding and estimation (judging a number by the nearest landmark) -
Rive Factors, divisors, and prime numbers (splitting a number into what divides it) -
Vie Comparing and ordering (magnitude — greater-than and less-than) -
Weld Number bonds (part-part-whole decomposition; making ten) -
Yoke Parity (even and odd numbers)
Ensemble stories — the cast together