I explain how the word "teen" in the "teen numbers" actually refers to ten. For example, fourteen means "four-ten", or ten plus four. Thinking of it that way, these "teen numbers" (thirteen, fourteen, fifteen, etc.) tie in neatly with place value.
We also practice with a hundred-chart, finding numbers ending in 5, whole tens, numbers in the 40s, and such.
If you cannot see the video above, click here for an alternative video player.
Math Mammoth Place Value 1 — workbook for 1st grade math
Math Mammoth Grade 1 curriculum