We open with a review of fractions on a number line, using the class number line and fractions of 1/4, 1/2, and 3/4. The focus is on the equal units that make up the number line - wholes, halves, fourths. Questions to probe students' understanding could be phrased as "prove your thinking", such as:
How do you know these are fourths?
How would you name fractions above 1?
Some students respond with 5/4 and 6/4. I open up the discussion to ask all students about how measurements are recorded in a mixed number format of 1 and 1/4 or 1 and 3/4. I do not use the mathematical terminology of mixed numbers at this point with the students. Today, the focus is on building measuring skills.
Students are using rulers that I've printed. Using a printed ruler allows me to control the unit sizes (and the visual clutter) because our focus in 3rd grade does not go beyond fourths. I got my ruler from Online Ruler. There are many free choices available, pick what works best for your class.
Introduce the ruler. They do not have fraction marks, but students need to be able to understand the different fractions. I emphasize the standard form of measuring would be to use the term and mathematical representation - 1/2 - rather than 2/4. Additional review of these fraction marks is reinforced through the use of the large classroom number line. Spending time to make sure the students can read measurements on a ruler is necessary for the success of this lesson and future lessons on measurement including Jumping Into Measurement lessons.
I demonstrate selecting different items and taking careful, precise measurements using a ruler. This is projected on the screen for everyone to see. I ask the students to identify the measurement, first reading it off the screen and then by writing it on their whiteboards. This gives me a formative assessment during the lesson and helps me to determine when the students are ready to begin working on their own.
Once students can easily name measurements on their rulers, they begin to locate items within the classroom that are between the ranges of <1 inch, 1-2 inches, 2-3 inches, 3-4 inches, 4-5 inches, and 5-6 inches. These include items such as paper clips, books, erasers, and various math manipulatives including shape blocks and unifix cubes. I emphasize finding items that are not at exact inch measurements because that's "real world" measurement.
As they locate items for each range, the students also record the name of the item and the measurement of the item. Labels count! If I see a measurement written without the units, I inquire, "What is that? Three and a half cats? Squirrels?" I require the students to use the inch mark notation of 3 1/4". Each student works on their own so that he/she has a chance to use the ruler.
To close the lesson, the students share with a partner items selected, and their measurements. The second student measures the item and states the measurement. The first student checks their measurement to see if the measurement data matches, and if not, the students work together to revise and record an accurate measurement.