Lesson plan Grade 3 Math

Foxglove Elementary's Fountain Fill-Time: An Elapsed-Time Lesson

A grade 3 lesson where students use start and end times to find how long fountains take to fill Field Day coolers, using a number line.

Grade: Grade 3
Subject: Math
Material: Lesson plan
Time: 45 min
Prep: Low prep
Materials: Clock or stopwatch with a minute display, Chart paper for a number-line diagram, Student handout with the two independent practice problems, Index cards for the exit ticket

Standards

3.MD.A.1 Common Core Math

Tell and write time to the nearest minute and measure time intervals in minutes. Solve word problems involving addition and subtraction of time intervals in minutes, e.g., by representing the problem on a number line diagram.

How this material aligns: Students find two fountains' fill times to the nearest minute from given start and end times and solve the guided and independent practice problems by finding elapsed time on a number-line diagram.

All materials for 3.MD.A.1 →

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This material is in the public domain (CC0) and may be copied, edited, and shared freely, without attribution. Updated 2026-07-16.

Objectives

Students will measure elapsed time to the nearest minute using a start time and an end time.
Students will solve addition and subtraction word problems about time intervals using a number-line diagram.
Students will compare two elapsed times to decide which event took longer.

Vocabulary

Key words: elapsed time, number line, interval, minute

Teacher overview

At the fictional Foxglove Elementary School, the class is helping fill two water cooler jugs before Field Day: one from the gym fountain and one from the cafeteria fountain. Students use the clock time when each fountain started filling and the clock time when it stopped to find how many minutes each fill took. A common misconception in this lesson is that elapsed time can be found by simply subtracting the smaller clock number from the larger one without accounting for the hour; walking the interval out on a number line, minute by minute, keeps that error visible and correctable.

Procedure

Hook (5 min): Ask students how long they think it takes to fill a cooler jug at the drinking fountain: a few seconds, a few minutes, or longer? Take three or four guesses and write them on the board without correcting them yet.

Direct instruction (10 min): Tell students that this morning, the gym fountain started filling a cooler at 8:05 and finished at 8:14. Draw a number line on chart paper from 8:05 to 8:14, marking each minute, and count the jumps together to show the fill took 9 minutes. Then reveal that the cafeteria fountain started at 8:20 and finished at 8:26. Draw a second number line and count 6 minutes. Ask: which fountain filled the cooler faster, and by how many minutes? (9 − 6 = 3 minutes faster.)

Guided practice (15 min): In pairs, students find the fill time for a third fountain, by the office, which started at 10:52 and finished at 11:05. Pairs draw their own number line from 10:52 to 11:05 and count the minutes (13 minutes). Then they answer: how many more minutes did the office fountain take than the gym fountain took this morning (13 − 9 = 4 minutes more)? Circulate and check that every pair's number line has 13 evenly spaced jumps before they move to the subtraction.

Independent practice (10 min): Each student answers two problems on the handout: (1) If the cafeteria fountain starts filling at 1:15 p.m. and takes its usual 6 minutes, what time will it finish? (2) If the class fills the gym cooler (9 minutes) and then immediately the cafeteria cooler (6 minutes) with no pause between them, how many total minutes will filling both coolers take?

Closure / exit ticket (5 min): On an index card, students solve one more problem: a fourth fountain, by the library, starts filling at 11:00 and finishes at 11:11. How many minutes did it take, and was that faster or slower than the gym fountain's 9 minutes? Collect the cards and scan for whether students counted the interval correctly before dismissal. A show of hands ("faster" or "slower") gives a quick whole-class check for understanding.

From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.

Answer Key

Answer: 1:21 p.m.
Starting at 1:15 p.m. and adding the usual 6-minute fill time: 1:15 + 6 minutes = 1:21 p.m.
Answer: 15 minutes.
Filling the gym cooler takes 9 minutes and the cafeteria cooler takes 6 minutes. Back to back with no pause: 9 + 6 = 15 minutes.
Exit ticket answer: 11 minutes, slower.
From 11:00 to 11:11 is 11 minutes. Compared to the gym fountain's 9 minutes, 11 − 9 = 2 minutes slower.

Differentiation

Support (below grade level)

Give these students a pre-drawn number line with every minute already marked as a tick, so they only need to count jumps rather than draw and space the line themselves. Keep all start and end times within the same hour so no problem requires crossing from one hour into the next.

Extension (above grade level)

Ask students to find the fill time for a fifth fountain that starts at 9:47 and finishes at 10:03, which crosses the hour mark. Have them explain, in writing, the strategy they used to count minutes across the hour boundary instead of within a single hour.

ELL supports

Pre-teach "start," "finish," and "elapsed time" using a simple picture timeline with the words labeled in English and, where possible, in students' home languages. Allow students to show elapsed time by drawing tally marks for each minute on the number line instead of writing a subtraction equation, then translate the tally count into the equation together as a class.

Extensions

Have students time how long it actually takes their own classroom sink or a hallway fountain to fill a one-liter bottle, in seconds this time rather than minutes, and discuss why a bottle fills so much faster than a whole cooler jug. This connects the lesson's minute-scale reasoning to a shorter, directly observable interval.