This is a reasonable preliminary study but the conclusions drawn by it are not justified. Some students were told they were special, and then got to leave their (possibly poorly performing and depressing) schools and spend considerable time being personally mentored by experts in their field while spending the day in a nice environment.

Perhaps we replace museum with "biology lab", "baseball camp", "robotics research", "skateboarding lessons", or any of a number of other things where students are specially selected to be taken to an interesting new location and tutored by experts in small groups. Would we get similar results, or is exposure to art in particular what is responsible for these results? That is not determined by this study and would need to be before making such dramatic claims.

Also, the way they assessed critical thinking skills here is questionable. Students went to the museum and art was discussed in a particular way, talking about symbols and analysis of paintings and so forth. Then the students who went to the museum and heard this, and those who didn't, were asked to write an essay about a painting. The ones who had been to the museum and heard people talking about paintings in the way the "good" essays were scored did better than those who had not been given exposure to an example of how people are expected to talk about art in an academic context. This is not a measure of critical thinking skills at all! It is a measure of who went to the museum and listened. To measure improvements in critical thinking skills, the content of the essay should not have been directly specifically linked to the type of content they were exposed to during the field trips, because as such the test is also measuring their exposure to that content (art criticism and analysis) and its style. To compare to baseball again, it would be like sending kids to baseball camp and then testing those who went to camp against those who didn't in a test where they were asked to write an essay about promising 2014 rookie players, and then claiming that good results in essays about baseball from the baseball camp goers was evidence the baseball camp created gains in general critical thinking skills. Maybe it did but such a test tightly connected to the particular subject matter that one group was exposed to and the other was not is not a reasonable way to assess general critical thinking skills.