2.9.E

Math2nd Grade

The Standard

determine a solution to a problem involving length, including estimating lengths

Texas Essential Knowledge and Skills for Mathematics

Teacher's field guide

What Students Need to Do: Students decide whether to add, subtract, or compare measurements in a word problem. They estimate first, then use a drawing, number line, or equation to find and check an answer.
What Mastery Looks Like: A student identifies the known and unknown lengths, chooses the correct operation, and shows an equation or drawing. The estimate is reasonable, and the exact answer includes the correct unit.
Common Misconceptions: Students may treat an estimate as a random guess instead of using a nearby benchmark. They may mix centimeters and inches, choose addition when finding a difference, or leave units off the answer.
How to Assess It: Exit ticket: A ribbon is 38 centimeters long. Mia cuts off 16 centimeters. Estimate the length left, then find the exact answer and label it.

Lesson moves

Give pairs rulers and yarn. Students estimate each piece, measure it, then find how much longer one piece is.
Ask, "When would an estimate be enough, and when would you need an exact length?" Students write one example of each.
Play Length Problem Sort. Students match story cards to addition, subtraction, or comparison equations, then solve and label each answer.
Estimate and measure book widths, then calculate whether three chosen books will fit in a 30-centimeter shelf space.

Keep exploring

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