Why are you asking "statute in Texas law"? I thought I was pretty clear it was a Supreme Court ruling. (I did use an unqualified acronym for it, SCOTUS, so if that's the source of the confusion I apologize.)
Anyway, Dover v. Kitsmiller is one of the well-known and recent ones, but never reached the SCOTUS. One that did, though, is Freiler v. Tangipahoa Parish Board of Education. That explicitly barred even the mention of creationism as an "alternative" to evolution, let alone its explicit teaching. That went all the way to the SCOTUS after the school board was ruled against, and the SCOTUS declined to consider a reversal, so that decision became final, and with the Supreme Court refusal to reverse, became caselaw for the entire land.
Since Supreme Court decisions are sovereign over Texas law, that makes it illegal in Texas or anywhere else in the US. That stems, of course, ultimately, from the First Amendment (government may not establish/endorse religion), and the Fourteenth (rights amendments applied to state/local law as well as federal). Those are ultimately the laws at play here. I'm not sure why you think Texas law would have anything to do with it.
I'm also unsure why you think "(my) personal definitions" have force under Texas law, or where you think I claimed that. But the Supreme Court of the United States, and the US Constitution, most certainly do have legal and binding force in Texas.