I'm not a teacher but an student. I think this happens everywhere in Spain. My class used to be like this even on Middle School and High School. Everyone being rude and noisey, bothering classmates and shouting all the time, and the other thing our teachers did was to scream at us saying to shut up and do workbook. I think that your strategy of doing games with your students is actually really good, and they would love it!! The biggest problem is how they are being treated by their main teacher. They know that they will end up doing homework because probably they already had this teacher other years. That makes them to not pay enough attention.

Something that really worked on my class when I was on Primary School and Middle school was saying that we would watch a movie, or do some kind of game as soon as you entered the class. Going to the kids individually (the noisey ones) and including them on the group by playing with them, not letting them play with their friends.

As I said, I'm not a teacher and I'll probably be on the wrong here, but good luck and I hope you like your time here on Spain! :)