Here in Washington State, it is in the Constitution: "It is the paramount duty of the state to make ample provision for the education of all children residing within its borders, without distinction or preference on account of race, color, caste, or sex."

personally to me it is inseparable part of basic human rights. Legally-wise, the US goes even further - the basic education is compulsory.

Is there a particular philosophy or school of thought (no pun intended) that leads you to this conviction? There's a difference between saying "I personally believe that everyone deserves a free public education," and saying education is a "guaranteed right that the government is supposed to deliver upon."

Or are you just saying that currently education is required by law and should remain so?

ok, you're right that compulsory education isn't equivalent to a "guaranteed right" - in the latter one can opt out, while in the former a child is truely guaranteed to receive it. In both cases, be it compulsion or pure right, the government is, obviously, responsible for the delivery upon it to happen.

Understood. You were referring to what is, not stating an opinion on what should be. The term "right" can get very confusing (e.g. "God-given" vs "constitutional").