If a student is not going to graduate because they failed the TAKS test do still have attend school in state of Texas?

In Texas, students must attend school until they turn 16, regardless of whether they pass the TAKS (or STAAR, its successor). Failing the TAKS/STAAR doesn't excuse them from compulsory attendance. They will likely need to repeat the grade or participate in remediation programs to improve their scores and eventually graduate.