A byproduct of having opposite gendered children is that I tend to spend a lot of time thinking about their differences, in the context of being a boy or girl. Having no personal experience being a boy, I often feel more in tune with the way Helen might see the world, and how the world sees Helen. I find myself brushing off things I can't explain easily about Connor as "it must be the difference between boys and girls". Sometimes, this is probably warranted. Other times, I'm probably confusing gender differences with any number of other things.
Last year, Helen spent most of her time playing with the boys in her class. And while she's still quite close to at least one boy in the class, and enjoys having playdates with a few different boys in her class, her teacher reports that most of the time, she plays with the girls this year. In some ways this makes sense, because Helen is definitely a girly-girl in her clothing choices and around our house, she loves to play with babies and other traditional "girl" things. Playing with the girls at school represents a huge change for Helen.
My very simplistic observation is that playing with girls is a lot more difficult than playing with boys. When I observe the boys playing on the playground at Connor's school, they don't waste a lot of time choosing sides, explaining rules, or figuring out how they'll all fit together. They run outside, divide roughly in half, and start playing some sort of game focused on a ball. Everyone gets to play, and in many ways they play an every-man-for-himself style of game, with lots of cheering when someone from your team scores - even if that scoring effort is largely solo. They will occasionally stop a game to argue, but mostly there's enough people that want to keep playing that they just keep moving through disagreements that arise. Which is not to say there are no rules - these get debated mightily - once - and then they are accepted for many weeks. Or, a few competing sets of rules will develop and then the start of the game is a very simple statement of "we're playing by rule set 1", and everyone seems to understand that rule set 2 will be played the next day. Easy.
Girls, on the other hand, argue endlessly about what role each person will have, the fairness of that role, and will plan the play beforehand. Often, Helen will say "pretend you came up to me and asked me why my baby was crying" and the desired response is to walk up to her and say some variant of "oh my, your baby is crying". The person she's playing with may, or may not accept the assigned task, and when she rejects the task, a discussion over what will happen will ensue. The setup seems to be the focus of the play.
I can see benefits to both styles of play.
What I fail to understand with girls, however, is why they seem to constantly need to confirm that someone is their friend, how much one girl likes another, and whether someone is allowed to play that day. A mystery, for sure, and it makes me crazy.