It is not meant to be comprehensive for all possibilities in various parts of the U.S., but to provide some general guidelines.
The American School System
American schools usually have a "cutoff deadline," meaning that a child must meet the minimum age by a certain date. That varies from place-to-place; it might be the start of the school year in one city, October 1st, November 1st, November 15th, or some other date. It is rarely earlier than September or later than mid-November. The school ages below are the age children typically are AFTER meeting the cutoff deadline:
Kindergarten (optional in some areas) is for ages 5-6
First grade => ages 6-7
Second, Third, Fourth, Fifth, Sixth, Seventh and Eighth grade progress from there (the math is left to the reader). These are referred to as "XX Grade" and not "Grade XX."
There is some vagueness about how certain grades are grouped in various types of schools, depending on the school district:
* Kindergarten (or First Grade) through Eighth Grade is one form of Elementary School (also called Grade School)
* Kindergarten (or First Grade) through Sixth Grade is another, which is followed by Middle School (7th and 8th grade, sometimes also 9th grade). A grade 7-8 or 7-9 school is sometimes also called Junior High.
* Kindergarten (First Grade) through Fifth Grade is the last type, with Middle School then being 6th, 7th and 8th grade. (if there is a 6th grade in it, this school will never be called a Junior High)
High School is either 10th-12th grade OR 9th-12th grade, depending. These grades have alternate names in high school:
These designations repeat for colleges/universities, i.e., first year of college is Freshman year, last year is Senior year.
"Junior" or "Community" College: this is two-year institution that some students go to instead of regular college, typically due to poor grades or lack of money (or both), or not yet being certain what they want to do with their lives (in or out of college). More recently, students frequently choose to go to Junior/Community College to get their General Educational Requirements out of the way at a cheaper price, and then transfer the credits to a four-year institution (thus lowering the total cost of obtaining Bachelor's Degree from an accredited college/university).
Additional notes: Americans graduate from a grade or institution, and receive grades (not 'marks') on their homework. Someone with good grades has a good chance of going to college.
Wikipedia may offer more details on any of the subsections of this listing, and there is a LiveJournal community called little_details where you can ask questions about specific cutoff dates and school groupings for a particular U.S. region or city.