I was about to say that it should be, 'til or 'till, with the apostrophe, but a check of Merriam Webster online suggests otherwise:
People often ask which is the correct synonym of until: till, ’til, or
Many assume that till is an abbreviated form of until. Actually, it is
a distinctive word that existed in English at least a century before
until, both as a preposition meaning “to” and a conjunction meaning
“until.” It has seen continuous use in English since the 12th century
and is a perfectly legitimate synonym of until.
’Til and ’till are much newer words, having appeared in the language
only in the 19th and 20th centuries, respectively. Both are variant
spellings, either of until or of till. Writers of usage guides have
roundly condemned ’till as a barbarism (apparently because it seems to
have added a superfluous l to the end of until). ’Til, for its part,
has been deemed inappropriate in formal writing.
To sum up: until and till can be used freely and interchangeably, but
you will probably want to avoid ’till and use ’til advisedly.
As for the sentences you have there, by the standard of a native English speaker, they are perfectly acceptable to me.
One way you could clarify the second sentence would be to say,
I went to school through 10th Grade.
Using "until" or "till" leans more towards suggesting you stopped at the end of ninth grade as opposed to stopping at the end of tenth grade, though it's a bit ambiguous. It could mean you made it partway through, and a casual speaker might mean it to be that they completed tenth grade, though it would be less correct. Using, "Through" makes it more clear that you completed the grade.
For the first sentence, you could rephase it and ask,
"What grade did you make it through in school?"
and you would have the same clarity.