My son has just finished third grade. It's been a horrible year: the teacher has thrown more personal responsibilities on the students without ensuring good through-communications with the parents. This generated confusion and dismay!

The curriculum was unchallenging (Saxon) and my son learned nothing that he didn't already know.

What's horrible is that the teacher essentially put him on a shelf for the year.

My son asserts that his teacher visibly enjoyed teaching the girls in the class, but that the boys were not her focus.

I'm mad because he wasted a year, and in the process, developed a very negative attitude toward schoolwork.

Should I complain to the principal? Or will this just be disregarded?

If it were me, I wouldn't complain after the fact; the year is over and there's no getting that lost time back, and the principal is probably already aware of the teacher's problems.

However, I would be super vigilant at the start of next year, and speak up as soon as you see problems occurring.

I'd spend a little time over the summer getting ready to positively advocate when school starts next year. Figure out the normal procedure in your area, who you can talk to and who might be on your side. Look into possible subject acceleration and who you'd have to talk to about that. What data do you need to make it happen?

It's too late now for this year, but next year start over!

As I stated in the other thread, I'd instead recommend that you make a request for the kind of teacher that your son needs for next year.

It sounds like your son needs a teacher who:
Revels in teaching and challenging boys
Teaches personal responsibility for ones work with support on these skills throughout the year
Clearly communicates with parents to ensure continuity between school and home.