If your preschooler is ready to work on the
teen numbers, you can set out the “teens
board,” a Montessori activity. Our math
curriculum has us refer to these numbers as
“one ten and one” (11), “one ten and two” (12)
and so forth.
Also have the child set out a
string of 10 beads and one bead, a string of
ten beads and two beads, etc.
Teens board: http://www.montessorimaterials.org/Math/teens-board.pdf
Paper beads you can print out to work on ones and tens: http://www.montessorimaterials.org/Math/Bead1_10.pdf