grade level translation

I have been applying to several taching positions but in my research I have been confused with the grade levels.  What does transition, KS1, year 1 -year 5 translate into by american standards.  Is year 1 grade 1?  Any help on my confusion would be great.  Thanks!
Kristin

Yes.  It's the same thing-although the children will be slightly younger.  Year one is children who TURN six during the school year (from September to August) instead of children who are already six.  
Reception is  Kindergarten. (4 and 5 year olds).
Infant school is reception through year two and a junior school is usually years 3, 4, 5 and 6.

Thank you very much.  You confirmed and cleared up my questions.  

Sorry, didn't see all of your question.  Key Stage 1 is years one and two.  Ages 5-7  Key Stage 2 is years 3,4,5,and 6.  Ages 7-11.  Children are tested (SATS) at 7 (end of year two) and again at 11 (end of year six.)