U.S. school system, for the uninformed:
Age: Grade: Type of School in which you'd find one:
5-6 Kindergarten Pre-School or Kindergarten
6-7 First Grade Grade School
7-8 Second Grade Grade School
8-9 Third Grade Grade School
9-10 Fourth Grade Grade School or Middle School
10-11 Fifth Grade Grade School or Middle School
11-12 Sixth Grade Grade School or Junior High
12-13 Seventh Grade Grade School or Junior High
13-14 Eighth Grade Grade School or Junor High
14-15 Freshman (9th) High School
15-16 Sophomore (10th) High School
16-17 Junior (11th) High School
17-18 Senior (12th) High School
18-22 College and/or Already Working
To simplify: Most kids go FIRST to Kindergarten, where they learn ABC's and numbers, et cetera. THEN, they go on to Grade School. In small towns, Grade School continues up through the Eighth Grade, followed by High School. In large towns, the schools are divided up, usually with K-3 in "Grade School", 4+5 in "Middle School", and 6-8 in "Junior High", after which the JH kids go directly to High School, like everyone else.
There are some variations, but this is the 'standard' system in the U.S.
Tyler and I would be considered Seniors during this story, based on the ages that we gave.