"Why are you teaching me this? This is math class". How many times have you heard this? I wish all teachers would get on board with the concept that although we may teach one subject, we are still teachers. I think it is great when we can do cross curricular activities, and it helps the kids to better understand it. I add history and science questions in my bell ringers. You can always find something in every subject that you can link back to math.
My biggest thing is correcting the grammar of my kids! "Why is you always correcting me? This is Math". REALLY? Maybe that is why.
I have my kids write in math all time. I incorporate a 4 step plan, and the 4th step is to Justify what they did and why they did it. The kids do not like to justify, but it is such a great tool. I not only check for the math part of the justification, I check for the grammatical aspects as well. I think all teachers should incorporate writing in every subject, and we should all grade spelling, punctuation, and grammar.
I also have my students post discussions on the class wiki. I list a problem that they need to solve. They log in and write a discussion as to how to solve it. Since I am not able to see their written calculations, they must write in detail what they did, why they did it, and what the answer is. For some kids, this is a building process. The writing becomes more meaningful when you have discussions on the correct way to write. I do not count off points for the grammatical aspects of the writing every time they write, but I do at times. Maybe eventually, the corrections will sink in, and they will become better writers which will help them become better students....not just math students.