One of the preschool activities we enjoyed this winter/spring was adding one or two to single digits. Having seen what happens when you only give your kindergartener a day or two to master simple addition before moving on to the bigger numbers, I was quite willing to take it slow with manipulatives and repetition.
Still, I was surprised recently when Mia began spontaneously announcing random addition facts. We were driving together when inspiration struck. I recited the addition facts from 1 to 9 (1+1=2; 2+1=3, etc.) in numerical order. Then I started over, still in numerical order, asking her fill in the sum. She was quite quick up through about seven. When she paused on the next number, I "helped" her by answering. She told me, "Don't say it Mom! I can figure it out!" Then she did. I'm so excited that she figured out the "rule" of plus one addition: the sum is the next higher number that follows the big number in the problem.