Squirt, here's what I found online:
http://www.hslda.org/docs/nche/000000/00000049.asp

If this information is current, it looks like in Texas it will be up to the individual school district.

Hi Squirt,
The last time I checked, partial homeschooling was not allowed in Texas.

Yes, through that website I linked above I found a bill that was introduced last legislative session that would have specifically allowed students access to public school programs. Apparently it was "left pending in committee."

What's interesting about Texas is that nothing is really required for homeschooling except having a written curriculum and teaching certain subjects. Homeschooling law appears to just be defined by case law, not a statute. That Home School Legal Defense Association website has a lot of good information. I had never seen it before today.