Looking at a piece of text and memorizing important dates is not all it takes to think critically. Some steps must be taken to read critically and improve critical thinking. There are several types of critical thinking, but what it boils down to is how people understand the text beyond what it says on paper. It takes some thinking and imagining all the "what ifs?"
I have been getting low grades on tests and essays because I am missing this factor. I am not putting forth that extra though, also I never let a problem marinate in my head, but that is something else that is very important. It is important to let your subconscious thinking do some of the problem solving.