Draw a rectangle on the blackboard. Ask the students how many blocks they see. Then divide the rectangle into ten equal units. Ask the children again how many blocks they see. Explain to them that the ten blocks they see are all part of the original rectangle that you drew. Ask for a volunteer, and tell him to shade, or color, one of the ten blocks. Tell the class that this is one tenth. Tell him to shade in two or three more, then ask the students how many tenths are now shaded.
Tell your students to hold up both their hands. Ask them how many fingers they have in total. Tell them to close their fists and then hold up only three fingers. Ask them how many tenths this represents. Continue the exercise with seven fingers, five fingers, etc.
Bring in a full-size candy bar or a large, soft cookie for each of your students. Have them divide the candy bar or cookie into ten equal parts. Help them practice counting in tenths by telling them to eat tenths of their treat. After telling them to eat three tenths, two tenths and five tenths, explain that they have now finished their treat because they ate all 10 tenths. Those 10 tenths count as 1 whole treat.
Give your students practice sheets with problems that require counting in tenths for homework, to reinforce the concept.