These are key questions that help to focus the learning. Guiding questions are included in the student investigations on the MathStar site.

What is an essential question ? Questions that probe for deeper meaning and set the stage for further questioning foster the development of critical thinking skills and higher order capabilities such as problem-solving and understanding complex systems. A good essential question is the principal component of designing inquiry-based learning.

What constitutes a good essential question? In general, the best essential questions center around major issues, problems, concerns, interests, or themes relevant to students' lives and to their communities. Good essential questions are open-ended, non-judgmental, meaningful and purposeful with emotive force and intellectual bite, and invite an exploration of ideas. Good essential questions encourage collaboration amongst students, teachers, and the community and integrate technology to support the learning process.

How do we write good essential questions? First, consider the focus of the unit or lesson activity. Ideas for a good essential question may stem from your students' particular interests in a topic (e.g. What makes a video game good?), community resources (How does pollution impact the Rio Grande River?), local curriculum expectations (e.g. Who was a great New Mexican leader?), or a topic suggested by the standards themselves (e.g. Where do waves come from?). Then, examine the theme or concept in the curriculum that must be addressed and brainstorm questions that you or the students believe would cause them to think about the concept without dictating the direction or outcome of their thinking (e.g. "Why is fighting bad?" contains its own answer, namely that fighting is bad). Finally, utilize the six typical queries that newspaper articles address: Who? What? Where? When? Why? and How? and add the word "good" in front of the theme or concept.

How do guiding questions assist the learner? Once an essential question has been identified and agreed upon by the learners, the next step might be to formulate a list of related questions that will assist the learner in answering the essential question. Often embedded within an essential question are subcategories that will generate questions that guide the learner's inquiry. For example, the essential question "What makes a video game good?" might lead to subcategories such as graphics, ease of use, violence, and audience appropriateness, and their subsequent questions like "How do graphics affect the quality of the game?" or "How does ease of use contribute to its overall rating?"

Here is more information and web sites related to guiding questions.

Essential Questions
Three Categories of Questions: Crucial Distinctions