Maryland Math 2.GR.C.8

Math2nd GradeGeometric Reasoning and Measurement

The Standard

Estimate and calculate elapsed time to the hour and half hour (e.g. If the school day begins at 8am and ends at 3 pm, the school day lasts 7 hours).

Maryland College and Career Ready Standards for Mathematics (2025) · WORK WITH TIME AND MONEY.

Teacher's field guide

What Students Need to Do: Students estimate how long it is between two times. They count hours and half hours on a clock to find the exact elapsed time.
What Mastery Looks Like: A student can show 9:30 to 11:00 as three half-hour jumps and say the time passed is 1 hour 30 minutes. They can check whether an estimate of about 2 hours makes sense.
Common Misconceptions: Some students subtract the clock numbers and miss an extra 30 minutes. Others count the starting time as a full hour or think two half hours make two hours.
How to Assess It: On an exit ticket, ask: “Art club starts at 1:30 and ends at 3:00. Estimate how long it lasts, then show half-hour jumps to find the exact time.”

Lesson moves

Give pairs paper clocks; have them move the hands from 9:00 to 11:30 in half-hour jumps and count each jump aloud.
Ask, “How long is it from 10:30 to 12:00, and why is it not two hours?”
Play a card match game: pair a start and end time, such as 1:00 to 3:30, with its elapsed time.
Post a library sign reading “Open 10:00 to 12:30” and have students estimate and calculate how long the library stays open.

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