Slaps decline with age

If you stand in the hallway as a column of kindergardeners walk by, and hold your hand out palm up, at waist level, about 89 percent of them will slap your hand. Some with great energy, some tepidly.

If you do this with 2nd graders, about 74 percent will slap your hand.

With 4th graders, about 65 percent, and with 8th graders 2 percent.

Why is this?