It is a bit unclear to me when someone says high school in the U.S. if they imply junior or senior or none of the above.
"High school" is the universally-accepted term in the US, and means four years before university. "Junior" high school is not a universal term, though exists in some areas. "Senior high school" is a term I've never heard before, appears uncited on that wikipedia page, and were I to say it to anyone I know they would look at me funny.
Also, prior to high school, kids are usually taking math and science classes at all times, so the absolute maximum would be one year without math and science.
That's good. (Although what is the purpose of the off year?) Question: when you say science what does that incorporate?