Students are usually 10 - 12 years old. Traditionally, sixth grade was the final year of elementary school. In the United States and Canada, sixth grade is ...
en.wikipedia.org/wiki/Sixth_grade

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Note added at 5 mins (2009-09-18 19:34:16 GMT)
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Los alumnos de sexto de Primaria de Madrid (11-12 años) se han sometido este ... 6. ¿Por qué número debes dividir 900 para obtener 30 como cociente? ... una encuesta entre los 25 alumnos de su clase para saber cuántos niños tienen algún ...
www.20minutos.es/noticia/377015

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Note added at 2 days18 hrs (2009-09-21 14:25:36 GMT)
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Sorry, I forgot to get back to this. "Elementary Schoo, 6th Grade" is valid for the USA. The equivalent is "Primary School, Year 6" for the UK.

Information about UK Primary School:

The National Curriculum applies to pupils of compulsory school age ... It is organised on the basis of four key stages.

Key stage 1: Ages 5-7 (Years 1-2)
Key stage 2: Ages 7-11 (Years 3-6)
Key stage 3: Ages 11-14 (Years 7-9)
Key stage 4: Ages 14-16 (Years 10-11).
http://curriculum.qcda.gov.uk/key-stages-1-and-2/Values-aims...

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Note added at 2 days19 hrs (2009-09-21 14:56:45 GMT)
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YEAR SIX (6 ) in the UK system (10-11 years old, or more).