Kindergarten Rocks by Katie Davis (2008)
Dexter already knows everything there is to know about kindergarten. His big sister, Jessie, told him all about it. So Dexter is not scared. Not even a little bit. But his stuffed dog, Rufus, is scared. Actually, he’s terrified. But Dexter--er, Rufus--has nothing to fear: As he’ll soon find out, kindergarten rocks!