You did not say if you wanted UK, Australian, Canadian or North American English, they all have differences, but Secondary Education would be a good generic translation. "Ensino" is education, not school.

Actually in Brazil they renamed this as "ensino medio" in 2003. It is only three years, whereas American high school is four years. If you want to call it secondary school, that will work outside the USA. It will puzzle the non-cosmopolitan Americans.

From notes I kept in a private academic terms glossary re 2003:
1o. grau: the first eight years of school (ensino fundamental) - which in 2008 was increased to 9 years by incorporating the very old pre-primario.
2o. grau: the three years after that (ensino médio)
3o. grau: university (what is called undegraduate degree in the U.S.) but people rarely refer to university as “terceiro grau” – more often it’s “nivel superior”


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Note added at 2 days1 hr (2013-03-07 20:26:40 GMT) Post-grading
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For Europe the term secondary school is better, as the asker decided.