Getting Started 
Misconception/Error The student is unable to correctly describe the twodimensional figures that result from slicing threedimensional figures. 
Examples of Student Work at this Level The student:
 Describes the two parts of the cone that result from the slicing rather than a twodimensional cross section of the cone.
 Describes incorrect plane figures.
The student may also confuse some or all of the terms: horizontal, vertical, parallel, perpendicular.

Questions Eliciting Thinking What is the difference between a twodimensional figure and a threedimensional figure? Can you give me an example of each?
Do you know what cross section means? Can you imagine the cross section of the cone that is revealed by the slicing?
What does parallel (perpendicular) mean? 
Instructional Implications Review the difference between twodimensional and threedimensional figures. Provide the student with examples of figures to be classified as either twodimensional or threedimensional. Ask the student to classify the figures and identify the dimensions of each.
Consider implementing the CPALMS Lesson Plan Can You Cut It? Slicing ThreeDimensional Figures (ID 47309). This lesson guides the student to sketch and describe a twodimensional figure resulting from the horizontal or vertical slicing of a threedimensional figure. Be sure the student understands the difference between horizontal and vertical, parallel and perpendicular. Model horizontal and vertical slices. Define parallel and perpendicular, and then model parallel and perpendicular slices in relation to the base. If needed, review the features of a cone, and emphasize that the base is a circle which is described by its diameter or radius. If needed, provide additional experience with identifying and drawing twodimensional slices of threedimensional figures and describing their dimensions. Consider implementing this task again to assess if the student can sketch and describe the twodimensional cross section resulting from each slice. 
Making Progress 
Misconception/Error The student does not adequately describe the dimensions of the plane figure in terms of the dimensions of the original figure. 
Examples of Student Work at this Level The student can identify and draw the figures resulting from the described slices but:
 Is unable to describe their dimensions.
 Does not clearly describe how the dimensions compare to the original figure.

Questions Eliciting Thinking What do you mean by â€śhalf?â€ť Half of what?
To what part of the cone can you compare the circle? How does the circle compare to the base of the cone? How does the diameter of this circle compare to the diameter of the base?
What are the two dimensions of the triangle? To what part of the cone can you compare the base and height of the triangle? 
Instructional Implications Guide the student to relate the dimensions of the twodimensional figure to the dimensions of the original threedimensional figure. Model a concise comparison (e.g., the diameter of the circle is less than the diameter of the circular base of the cone). Provide additional opportunities to precisely describe cross sections of threedimensional figures. 
Got It 
Misconception/Error The student provides complete and correct responses to all components of the task. 
Examples of Student Work at this Level The student correctly identifies and draws the plane figures resulting from each slice, and describes each using specific dimensions. For example, the student says:
 The cross section is a triangle with a height equal to the height of the cone, and a base equal to the diameter of the circular base of the cone.
 The cross section is a circle with diameter smaller than the diameter of the circular base of the cone.
 The cross section is an ellipse.

Questions Eliciting Thinking Does the slice have to be in the middle (halfway) in order to be horizontal (vertical)? Can the horizontal slice be close to the base of the cone?
What happens to the horizontal slice as it gets closer and closer to the base of the cone? What happens to the slice as it gets closer and closer to the vertex of the cone? 
Instructional Implications Challenge the student with more complex figures such as a double cone and slices that are neither parallel nor perpendicular to the base.
Consider implementing the MFAS tasks Rectangular Prism Slices, Cylinder Slices, or Square Pyramid Slices (7.G.1.3), if not done previously. 