Bringing videos of actual women scientists into schools and having visits from actual women scientists have both been very successful in terms of breaking stereotypes. I've noticed that there have been changes in the media over the past several years. Women are often being portrayed as scientists on TV shows. TV has been identified as one of the strongest areas that shift perceptions about scientists and the sciences.
It's not happening enough. There are still so many stereotypes out there. If we're talking about it particularly from the perspective of the media, which can shift children's perceptions so strongly, I think it's important that actual scientists be represented in the media. For example, on a lot of science shows they have actors playing scientists. When you have an actor playing a scientist as the host of the show, they're more likely to make a stereotypical representation, because an actual scientist knows what it actually means to be in the sciences.