In the uk, there's primary school, which is reception to year six - that's also sometimes split into Infants ( reception to year two) and Juniors (year three to year six). That's followed by secondary school which is year seven to year eleven, and that's the end of compulsory education. After that you get sixth form, which is split in my town into first years - year twelve - and second years - year thirteen. At sixth form you take the exams necessary for going to university.
-Infants (also called Key Stage One)-
Reception - aged 4 to 5
Year one - aged five to six
Year two - aged six to seven
-Juniors (also called Key Stage Two)-
Year three - aged seven to eight
Year four - aged eight to nine
Year five - aged nine to ten
Year six - aged ten to eleven
At the end of year six, kids take exams called SATs, which help secondary schools sort classes by ability.
-Secondary school (Key Stage Three)-
Year seven - aged eleven to twelve
Year eight - aged twelve to thirteen
Year nine - aged thirteen to fourteen
At the end of year nine, you do more SATs to help determine which class you'll be in for your GCSEs.
-Secondary School (Key Stage Four)-
Year ten - aged fourteen to fifteen
Year eleven - aged fifteen to sixteen
At the end of year eleven, you take GCSE exams, which I think is the most basic qualification, required for pretty much anything. Some people leave education at sixteen, some do vocational courses such as hairdressing, and others go onto sixth form.
First years/year twelve - aged sixteen to seventeen
Second years/year thirteen - aged seventeen to eighteen
The ages of students at sixth form aren't as rigid as in school; you can switch between colleges if you don't like the qualification that you're doing, so if you start on a vocational course, you can at the end of the year change to a sixth form college and do a more academic subject and vice versa. In sixth form you take exams (there are several different types) and the grades from these are what you use to get a place at university.
Also, our school year runs from the start of September through to the middle of July