S.P.
Between what you have written here along with the bathroom break story from a few days ago, it seems to me you need to go above the principal's head to whatever is the governing body. School Board? District Administrator? What you have described is inexcusable.
Find out if Dallas has any kind of programs for gifted children.
It seems to me, a big city would have to have that kind of program.
Your son needs to be there, in a class for gifted children, not where he is now. Please let us know what happens.
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Adding:
Make a detailed list . . . no extraneous items,
just point-by-point . . . the bathroom story, the baby work,
the rigid attitude of the teacher, including how she spoke to you, et al.
Write to whoever/whatever is the governing body/person,
including this list of inappropriate actions toward your son.
Mention that he already knows multiplication/division, etc.,
and his experience in his previous school.
You require that he not be stuck in this classroom with this teacher,
for his mental and emotional wellbeing.