Quick Answer. An experimental variable is something that a scientist changes during the course of an experiment. It is distinguished from a controlled variable, which could theoretically change, but the scientists keep constant. Continue Reading.
While you were pregnant, your baby developed tooth buds, the foundation for baby teeth (also called milk teeth). Very rarely, a baby is born with a tooth or two, or grows a tooth in the first few weeks of life. But the vast majority of babies sprout their first tooth sometime between 4 and 7 months old.
After that first tooth breaks through, more and more teeth begin to appear. Most kids have their first set of teeth by the time they are 3 years old. These are called the primary teeth, baby teeth, or milk teeth and there are 20 in all. When a child gets to age 5 or 6, these teeth start falling out, one by one. A primary tooth falls out because it is being pushed out of the way by the permanent tooth that is behind it. Slowly, the permanent teeth grow in and take the place of the primary teeth.