I like to start this lesson by watching the following video
After the video, we practice counting by tens to 100. I then randomly call on students and ask them to tell me the age of someone in their family. I write the numbers on the board as they are called out. After four or five, I then use the T chart to demonstrate the tens and ones place.
I have students use base ten blocks to model 35 and 36. Guide the students to think about their numbers:
Read the following problem to the class: Tony has 22 markers. Pat has 10 less markers than Tony. Jan has 10 more markers than Tony. How many markers does each child have?
I have students draw a picture to show how many markers each child has. Point out that there is a quicker way to solve our problem rather than writing or drawing it.
Explain that because the tens digit only changes by 1, we can find 10 more or 10 less by mentally adding or subtracting 1 to the number of tens.
I model this by selecting a number and asking students to determine what number is 10 more and what number is 10 less. For example – I write the number 33 on the board, and draw the tens and ones. Draw the number that is 10 more and 10 less.
For the independent practice portion, I give each student 2 number cubes (dice). They roll the dice and record the two digit number. Then then draw the number using tens and ones, and determine the number that is 10 more and 10 less.
For those struggling students, I pull them into a small group and we use a hundred chart and practice counting by tens.
I also give them base ten blocks to help with building their numbers on the independent activity.. I write a number on a white board and ask students to model the number. For example:
Then have students add one more ten to their model and ask “What number is 10 more than 47?” Have students go back to the original number (47) and take away one ten, ask “What number is 10 less than 47?”
To close out this lesson, I number index cards with numbers that are three cards in each set. The cards are numbered so that there are three in each set – the base number, 10 more, and 10 less (for example: the first set of cards would be 65, 75, 85; the second set would be 35, 45, 55; etc.)
Each student gets 1 card. Then then walk around and find their corresponding cards that go with their set.