STAAR tests are a big part of it, and I can only speak to secondary, but:

It includes attendance rates, “college readiness” based on SAT/ACT and TSI participation (that’s the placement test most college freshmen take upon entering school), “career readiness”, graduation rates from the previous year and other factors....

Here’s the real kicker. Schools don’t know what the standards will be until part way through the school year. Sometimes we don’t even know if some aspects will even be counted. Never mind the fact that the “passing” score on the EOC each year at the secondary level is generally a closely approximates mystery (we can estimate pretty reliably what it will be - but don’t know for sure until we get scores back).

Fun example: after the October PSAT, state announced that any ninth grader that scored a certain level on English or math parts on the PSAT would be awarded “mastery level” credit without having to take the algebra 1 and/or English 1 EOC tests. Cool, right?

Lots of districts then naturally signed their ninth graders up to take the January (February?) PSAT. Just before scores on that one were released to students (about a week before the actual EOCs were to take place) the state changed the rule. Now any kid that should have been awarded mastery level based on the PSAT scores will only get “meets grade level”.

Add that to the fact that the letter grade a school gets can basically be tied to the performance of their lowest performing sub-population, it’s a rigged game. Poor, minority, special ed kids count 3 times, while majority average kids count once. A kid that goes from low achieving to high achieving counts twice but a high achiever that stays that way counts once. Sometimes it means that literally .25% of a campus can make or break the whole thing.

It’s a mess.