I think the problem you're running into is a common one for teachers of literature, the task of drawing up a lesson plan that seeks to isolate a skill, such as drawing conclusions. Unlke math, which is very linear, and even science and social studies which tend to be more content-based, studying...
I think the problem you're running into is a common one for teachers of literature, the task of drawing up a lesson plan that seeks to isolate a skill, such as drawing conclusions. Unlke math, which is very linear, and even science and social studies which tend to be more content-based, studying literature requires a spiraling of skills that are probably never truly "mastered". Furthermore, the idea of modeling, guided and independent practice might work when teaching a reading skill such as using context clues, but critical thinking is a much broader skill that requires ongoing practice.
Your first task should probably be to review the specific standards for your state and figure out how critical thinking/drawing conclusions is written into them. Drawing conclusions, analyzing, inferring--all of these terms tend to show up in grade level expectations and other curriculum documents, and in some ways are closely related. Keep in mind that just around the corner are the new Common Core guidelines that will require most states to more or less rewrite their entire curricula in the next year or so--or so they say.
Perhaps for this novel, you could first have your students do a character study of the main character, focusing on direct description, what the character says and does, and how others react to the character. From there you could probably develop some short answer/essay type questions that would require critical thinking/drawing conclusions/inferring. I haven't read this particular book, but in any work of literature, when I teach inferring, I ask the students what they would think if someone came into the room dripping wet. They almost always say that the person would have come in from the rain. Then we talk about one's experiences and why they would all automatically conclude that the person came in from the rain and didn't just get out of the shower--because in their experiences, people don't normally take showers at school, and if they (like in gym) they wouldn't normally show up in the middle of class dripping wet.
The important thing about drawing conclusions and making inferences is that the student be able to explan/defend their ideas. I always tell my students that just about anything they can come up with will work--IF they can defend their ideas with examples and evidence from the text. And again, this is a dfficult skill to isolate; it requires internal reseach into the text to come up with evidence, and an understanding of the context of the story. I think your best bet on this topic/skill would be to come up with a list of questions that require more than a yes/no/one word answer; you might consult the higher levels of Bloom's Taxonomy for some ideas on writing "higher order" thinking questions.