What are the age groups for elementary middle and high school?

Well, it depends because different school districts have the grades grouped differently. Most commonly, it goes like this:

Elementary School: Kindergarten through 5th grade (ages 5-11)

Middle School: 6th through 8th grade (ages 11-14)

High School: 9th through 12th grade (ages 14-18)

But sometimes it's:

Elementary: Kindergarten through 6th grade (ages 5-12)

Middle: 7th and 8th grade (ages 12-14)

High: 9th through 12th grade (ages 14-18)

Or

Elementary: Kindergarten through 4th grade (ages 5-10)

Middle: 5th through 8th grade (ages 10-14)

High: 9th through 12th grade (ages 14-18)

And, this used to be the norm back in the older days, and is not common anymore, but some school systems do still do it like this:

Elementary: Kindergarten through 6th grade (ages 5-12)

Junior High (not middle school): 7th through 9th grade (ages 12-15)

High School: 10th through 12th grade (ages 15-18)